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 $170.48   13.768%   $193.9517   $193.95   $193.95   $194.00  
  Purchase #2 $84.79   4.454%   $88.5665   $88.57   $88.55   $88.60  
  Purchase #3 $198.44   10.863%   $219.9965   $220.00   $220.00   $220.00  
  Purchase #4 $250.94   11.607%   $280.0666   $280.07   $280.05   $280.10  
  Purchase #5 $220.48   5.236%   $232.0243   $232.02   $232.00   $232.00  
  Purchase #6 $24.69   5.819%   $26.1267   $26.13   $26.15   $26.10  
  Purchase #7 $170.53   13.298%   $193.2071   $193.21   $193.20   $193.20  
  7 purchase totals = $1,120.35       $1,233.9394   $1,233.95   $1,233.90   $1,234.00