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 $32.94   9.169%   $35.9603   $35.96   $35.95   $36.00  
  Purchase #2 $20.95   12.522%   $23.5734   $23.57   $23.55   $23.60  
  Purchase #3 $112.79   11.753%   $126.0462   $126.05   $126.05   $126.00  
  Purchase #4 $89.57   4.758%   $93.8317   $93.83   $93.85   $93.80  
  Purchase #5 $187.84   11.609%   $209.6463   $209.65   $209.65   $209.60  
  Purchase #6 $64.41   6.531%   $68.6166   $68.62   $68.60   $68.60  
  Purchase #7 $5.84   9.145%   $6.3741   $6.37   $6.35   $6.40  
  7 purchase totals = $514.34       $564.0486   $564.05   $564.00   $564.00