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 $65.65   9.137%   $71.6484   $71.65   $71.65   $71.60  
  Purchase #2 $69.68   4.830%   $73.0455   $73.05   $73.05   $73.00  
  Purchase #3 $112.89   9.410%   $123.5129   $123.51   $123.50   $123.50  
  Purchase #4 $177.68   5.319%   $187.1308   $187.13   $187.15   $187.10  
  Purchase #5 $73.75   12.659%   $83.086   $83.09   $83.10   $83.10  
  Purchase #6 $192.84   3.771%   $200.112   $200.11   $200.10   $200.10  
  Purchase #7 $80.44   3.198%   $83.0125   $83.01   $83.00   $83.00  
  7 purchase totals = $772.93       $821.5481   $821.55   $821.55   $821.40