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 $77.91   8.697%   $84.6858   $84.69   $84.70   $84.70  
  Purchase #2 $60.51   3.846%   $62.8372   $62.84   $62.85   $62.80  
  Purchase #3 $205.66   6.447%   $218.9189   $218.92   $218.90   $218.90  
  Purchase #4 $126.98   3.644%   $131.6072   $131.61   $131.60   $131.60  
  Purchase #5 $87.61   10.559%   $96.8607   $96.86   $96.85   $96.90  
  Purchase #6 $52.53   11.306%   $58.469   $58.47   $58.45   $58.50  
  Purchase #7 $139.51   5.845%   $147.6644   $147.66   $147.65   $147.70  
  7 purchase totals = $750.71       $801.0432   $801.05   $801.00   $801.10