Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $89.45   13.502%   $101.5275   $101.53   $101.55   $101.50  
  Purchase #2 $129.29   9.564%   $141.6553   $141.66   $141.65   $141.70  
  Purchase #3 $124.57   6.671%   $132.8801   $132.88   $132.90   $132.90  
  Purchase #4 $180.83   9.529%   $198.0613   $198.06   $198.05   $198.10  
  Purchase #5 $156.53   4.663%   $163.829   $163.83   $163.85   $163.80  
  Purchase #6 $163.52   11.133%   $181.7247   $181.72   $181.70   $181.70  
  Purchase #7 $211.37   12.492%   $237.7743   $237.77   $237.75   $237.80  
  7 purchase totals = $1,055.56       $1,157.4522   $1,157.45   $1,157.45   $1,157.50