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 $87.94   8.454%   $95.3744   $95.37   $95.35   $95.40  
  Purchase #2 $32.72   11.602%   $36.5162   $36.52   $36.50   $36.50  
  Purchase #3 $80.41   9.513%   $88.0594   $88.06   $88.05   $88.10  
  Purchase #4 $55.45   8.520%   $60.1743   $60.17   $60.15   $60.20  
  Purchase #5 $57.61   5.279%   $60.6512   $60.65   $60.65   $60.70  
  Purchase #6 $162.55   12.153%   $182.3047   $182.30   $182.30   $182.30  
  Purchase #7 $75.42   11.155%   $83.8331   $83.83   $83.85   $83.80  
  7 purchase totals = $552.10       $606.9133   $606.90   $606.85   $607.00