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 $60.60   12.484%   $68.1653   $68.17   $68.15   $68.20  
  Purchase #2 $208.43   6.373%   $221.7132   $221.71   $221.70   $221.70  
  Purchase #3 $132.57   3.367%   $137.0336   $137.03   $137.05   $137.00  
  Purchase #4 $104.96   12.413%   $117.9887   $117.99   $118.00   $118.00  
  Purchase #5 $232.54   9.251%   $254.0523   $254.05   $254.05   $254.10  
  Purchase #6 $153.58   6.517%   $163.5888   $163.59   $163.60   $163.60  
  Purchase #7 $180.50   9.208%   $197.1204   $197.12   $197.10   $197.10  
  7 purchase totals = $1,073.18       $1,159.6623   $1,159.66   $1,159.65   $1,159.70