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 $41.45   12.743%   $46.732   $46.73   $46.75   $46.70  
  Purchase #2 $94.59   11.560%   $105.5246   $105.52   $105.50   $105.50  
  Purchase #3 $244.30   6.494%   $260.1648   $260.16   $260.15   $260.20  
  Purchase #4 $219.35   12.287%   $246.3015   $246.30   $246.30   $246.30  
  Purchase #5 $103.61   7.186%   $111.0554   $111.06   $111.05   $111.10  
  Purchase #6 $21.57   11.253%   $23.9973   $24.00   $24.00   $24.00  
  Purchase #7 $208.90   8.745%   $227.1683   $227.17   $227.15   $227.20  
  7 purchase totals = $933.77       $1,020.9439   $1,020.94   $1,020.90   $1,021.00