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 $208.82   8.865%   $227.3319   $227.33   $227.35   $227.30  
  Purchase #2 $211.55   11.582%   $236.0517   $236.05   $236.05   $236.10  
  Purchase #3 $123.78   11.713%   $138.2784   $138.28   $138.30   $138.30  
  Purchase #4 $138.43   12.320%   $155.4846   $155.48   $155.50   $155.50  
  Purchase #5 $42.30   3.872%   $43.9379   $43.94   $43.95   $43.90  
  Purchase #6 $158.59   10.344%   $174.9945   $174.99   $175.00   $175.00  
  Purchase #7 $183.78   10.531%   $203.1339   $203.13   $203.15   $203.10  
  7 purchase totals = $1,067.25       $1,179.2129   $1,179.20   $1,179.30   $1,179.20