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 $208.39   7.790%   $224.6236   $224.62   $224.60   $224.60  
  Purchase #2 $214.28   5.393%   $225.8361   $225.84   $225.85   $225.80  
  Purchase #3 $136.96   7.406%   $147.1033   $147.10   $147.10   $147.10  
  Purchase #4 $59.35   12.272%   $66.6334   $66.63   $66.65   $66.60  
  Purchase #5 $93.59   11.373%   $104.234   $104.23   $104.25   $104.20  
  Purchase #6 $158.52   7.651%   $170.6484   $170.65   $170.65   $170.60  
  Purchase #7 $101.40   5.867%   $107.3491   $107.35   $107.35   $107.30  
  7 purchase totals = $972.49       $1,046.4279   $1,046.42   $1,046.45   $1,046.20