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 $63.36   8.801%   $68.9363   $68.94   $68.95   $68.90  
  Purchase #2 $189.59   9.503%   $207.6067   $207.61   $207.60   $207.60  
  Purchase #3 $242.85   12.145%   $272.3441   $272.34   $272.35   $272.30  
  Purchase #4 $157.34   9.310%   $171.9884   $171.99   $172.00   $172.00  
  Purchase #5 $124.45   4.849%   $130.4846   $130.48   $130.50   $130.50  
  Purchase #6 $156.57   4.618%   $163.8004   $163.80   $163.80   $163.80  
  Purchase #7 $37.66   7.849%   $40.6159   $40.62   $40.60   $40.60  
  7 purchase totals = $971.82       $1,055.7764   $1,055.78   $1,055.80   $1,055.70