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 $129.81   12.544%   $146.0934   $146.09   $146.10   $146.10  
  Purchase #2 $32.79   7.804%   $35.3489   $35.35   $35.35   $35.30  
  Purchase #3 $247.96   11.259%   $275.8778   $275.88   $275.90   $275.90  
  Purchase #4 $40.51   7.600%   $43.5888   $43.59   $43.60   $43.60  
  Purchase #5 $120.32   13.859%   $136.9951   $137.00   $137.00   $137.00  
  Purchase #6 $230.29   6.858%   $246.0833   $246.08   $246.10   $246.10  
  Purchase #7 $56.81   13.304%   $64.368   $64.37   $64.35   $64.40  
  7 purchase totals = $858.49       $948.3553   $948.36   $948.40   $948.40