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 $14.85   10.754%   $16.447   $16.45   $16.45   $16.40  
  Purchase #2 $144.98   8.686%   $157.573   $157.57   $157.55   $157.60  
  Purchase #3 $132.96   7.592%   $143.0543   $143.05   $143.05   $143.10  
  Purchase #4 $106.78   8.227%   $115.5648   $115.56   $115.55   $115.60  
  Purchase #5 $95.85   3.290%   $99.0035   $99.00   $99.00   $99.00  
  Purchase #6 $165.26   11.295%   $183.9261   $183.93   $183.95   $183.90  
  Purchase #7 $78.89   4.647%   $82.556   $82.56   $82.55   $82.60  
  7 purchase totals = $739.57       $798.1247   $798.12   $798.10   $798.20