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 $215.67   8.617%   $234.2543   $234.25   $234.25   $234.30  
  Purchase #2 $219.98   12.519%   $247.5193   $247.52   $247.50   $247.50  
  Purchase #3 $198.82   9.178%   $217.0677   $217.07   $217.05   $217.10  
  Purchase #4 $150.38   7.636%   $161.863   $161.86   $161.85   $161.90  
  Purchase #5 $19.74   11.461%   $22.0024   $22.00   $22.00   $22.00  
  Purchase #6 $58.34   12.371%   $65.5572   $65.56   $65.55   $65.60  
  Purchase #7 $212.38   9.544%   $232.6495   $232.65   $232.65   $232.60  
  7 purchase totals = $1,075.31       $1,180.9134   $1,180.91   $1,180.85   $1,181.00