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 $68.84   7.201%   $73.7972   $73.80   $73.80   $73.80  
  Purchase #2 $132.41   8.819%   $144.0872   $144.09   $144.10   $144.10  
  Purchase #3 $203.65   9.610%   $223.2208   $223.22   $223.20   $223.20  
  Purchase #4 $235.30   4.783%   $246.5544   $246.55   $246.55   $246.60  
  Purchase #5 $154.57   10.226%   $170.3763   $170.38   $170.40   $170.40  
  Purchase #6 $235.94   12.431%   $265.2697   $265.27   $265.25   $265.30  
  Purchase #7 $128.55   4.237%   $133.9967   $134.00   $134.00   $134.00  
  7 purchase totals = $1,159.26       $1,257.3023   $1,257.31   $1,257.30   $1,257.40