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 $186.65   8.170%   $201.8993   $201.90   $201.90   $201.90  
  Purchase #2 $149.97   11.192%   $166.7546   $166.75   $166.75   $166.80  
  Purchase #3 $239.48   8.133%   $258.9569   $258.96   $258.95   $259.00  
  Purchase #4 $186.74   5.462%   $196.9397   $196.94   $196.95   $196.90  
  Purchase #5 $209.26   10.361%   $230.9414   $230.94   $230.95   $230.90  
  Purchase #6 $218.59   11.194%   $243.059   $243.06   $243.05   $243.10  
  Purchase #7 $143.34   8.258%   $155.177   $155.18   $155.20   $155.20  
  7 purchase totals = $1,334.03       $1,453.7279   $1,453.73   $1,453.75   $1,453.80