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 $65.84   13.523%   $74.7435   $74.74   $74.75   $74.70  
  Purchase #2 $130.27   5.154%   $136.9841   $136.98   $137.00   $137.00  
  Purchase #3 $156.44   4.268%   $163.1169   $163.12   $163.10   $163.10  
  Purchase #4 $228.60   11.676%   $255.2913   $255.29   $255.30   $255.30  
  Purchase #5 $181.53   6.629%   $193.5636   $193.56   $193.55   $193.60  
  Purchase #6 $46.26   12.189%   $51.8986   $51.90   $51.90   $51.90  
  Purchase #7 $70.97   6.872%   $75.8471   $75.85   $75.85   $75.80  
  7 purchase totals = $879.91       $951.4451   $951.44   $951.45   $951.40