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 $181.45   8.870%   $197.5446   $197.54   $197.55   $197.50  
  Purchase #2 $193.31   3.561%   $200.1938   $200.19   $200.20   $200.20  
  Purchase #3 $172.88   11.358%   $192.5157   $192.52   $192.50   $192.50  
  Purchase #4 $82.44   12.740%   $92.9429   $92.94   $92.95   $92.90  
  Purchase #5 $29.94   11.143%   $33.2762   $33.28   $33.30   $33.30  
  Purchase #6 $179.75   11.804%   $200.9677   $200.97   $200.95   $201.00  
  Purchase #7 $54.55   7.141%   $58.4454   $58.45   $58.45   $58.40  
  7 purchase totals = $894.32       $975.8863   $975.89   $975.90   $975.80