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 $176.86   13.653%   $201.0067   $201.01   $201.00   $201.00  
  Purchase #2 $73.35   8.800%   $79.8048   $79.80   $79.80   $79.80  
  Purchase #3 $91.83   13.819%   $104.52   $104.52   $104.50   $104.50  
  Purchase #4 $69.50   5.697%   $73.4594   $73.46   $73.45   $73.50  
  Purchase #5 $97.33   12.450%   $109.4476   $109.45   $109.45   $109.40  
  Purchase #6 $134.43   10.717%   $148.8369   $148.84   $148.85   $148.80  
  Purchase #7 $33.52   11.411%   $37.345   $37.35   $37.35   $37.30  
  7 purchase totals = $676.82       $754.4204   $754.43   $754.40   $754.30