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 $97.88   4.755%   $102.5342   $102.53   $102.55   $102.50  
  Purchase #2 $52.46   3.485%   $54.2882   $54.29   $54.30   $54.30  
  Purchase #3 $247.55   13.715%   $281.5015   $281.50   $281.50   $281.50  
  Purchase #4 $240.48   13.596%   $273.1757   $273.18   $273.20   $273.20  
  Purchase #5 $205.77   13.814%   $234.1951   $234.20   $234.20   $234.20  
  Purchase #6 $106.74   13.399%   $121.0421   $121.04   $121.05   $121.00  
  Purchase #7 $27.97   3.207%   $28.867   $28.87   $28.85   $28.90  
  7 purchase totals = $978.85       $1,095.6038   $1,095.61   $1,095.65   $1,095.60