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 $221.56   10.108%   $243.9553   $243.96   $243.95   $244.00  
  Purchase #2 $101.52   3.121%   $104.6884   $104.69   $104.70   $104.70  
  Purchase #3 $35.33   9.186%   $38.5754   $38.58   $38.60   $38.60  
  Purchase #4 $30.91   3.755%   $32.0707   $32.07   $32.05   $32.10  
  Purchase #5 $93.92   13.340%   $106.4489   $106.45   $106.45   $106.40  
  Purchase #6 $163.25   9.562%   $178.86   $178.86   $178.85   $178.90  
  Purchase #7 $235.79   4.250%   $245.8111   $245.81   $245.80   $245.80  
  7 purchase totals = $882.28       $950.4098   $950.42   $950.40   $950.50