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 $217.29   8.313%   $235.3533   $235.35   $235.35   $235.40  
  Purchase #2 $31.52   9.339%   $34.4637   $34.46   $34.45   $34.50  
  Purchase #3 $156.82   6.345%   $166.7702   $166.77   $166.75   $166.80  
  Purchase #4 $188.92   9.750%   $207.3397   $207.34   $207.35   $207.30  
  Purchase #5 $208.56   5.355%   $219.7284   $219.73   $219.75   $219.70  
  Purchase #6 $216.59   13.794%   $246.4664   $246.47   $246.45   $246.50  
  Purchase #7 $157.66   6.258%   $167.5264   $167.53   $167.55   $167.50  
  7 purchase totals = $1,177.36       $1,277.6481   $1,277.65   $1,277.65   $1,277.70