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 $83.27   11.618%   $92.9443   $92.94   $92.95   $92.90  
  Purchase #2 $242.89   10.427%   $268.2161   $268.22   $268.20   $268.20  
  Purchase #3 $51.73   7.817%   $55.7737   $55.77   $55.75   $55.80  
  Purchase #4 $76.89   4.721%   $80.52   $80.52   $80.50   $80.50  
  Purchase #5 $230.53   11.860%   $257.8709   $257.87   $257.85   $257.90  
  Purchase #6 $207.39   10.766%   $229.7176   $229.72   $229.70   $229.70  
  Purchase #7 $68.88   7.687%   $74.1748   $74.17   $74.15   $74.20  
  7 purchase totals = $961.58       $1,059.2174   $1,059.21   $1,059.10   $1,059.20