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 $96.58   5.295%   $101.6939   $101.69   $101.70   $101.70  
  Purchase #2 $238.83   8.759%   $259.7491   $259.75   $259.75   $259.70  
  Purchase #3 $202.57   6.551%   $215.8404   $215.84   $215.85   $215.80  
  Purchase #4 $13.29   6.174%   $14.1105   $14.11   $14.10   $14.10  
  Purchase #5 $136.96   7.331%   $147.0005   $147.00   $147.00   $147.00  
  Purchase #6 $169.90   4.731%   $177.938   $177.94   $177.95   $177.90  
  Purchase #7 $123.81   8.217%   $133.9835   $133.98   $134.00   $134.00  
  7 purchase totals = $981.94       $1,050.3159   $1,050.31   $1,050.35   $1,050.20