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 $156.67   13.251%   $177.4303   $177.43   $177.45   $177.40  
  Purchase #2 $88.34   3.534%   $91.4619   $91.46   $91.45   $91.50  
  Purchase #3 $36.45   9.382%   $39.8697   $39.87   $39.85   $39.90  
  Purchase #4 $29.28   8.840%   $31.8684   $31.87   $31.85   $31.90  
  Purchase #5 $29.90   4.687%   $31.3014   $31.30   $31.30   $31.30  
  Purchase #6 $46.41   3.839%   $48.1917   $48.19   $48.20   $48.20  
  Purchase #7 $57.84   5.837%   $61.2161   $61.22   $61.20   $61.20  
  7 purchase totals = $444.89       $481.3395   $481.34   $481.30   $481.40