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 $217.28   4.610%   $227.2966   $227.30   $227.30   $227.30  
  Purchase #2 $139.65   9.441%   $152.8344   $152.83   $152.85   $152.80  
  Purchase #3 $229.43   8.385%   $248.6677   $248.67   $248.65   $248.70  
  Purchase #4 $59.91   5.495%   $63.2021   $63.20   $63.20   $63.20  
  Purchase #5 $54.97   12.374%   $61.772   $61.77   $61.75   $61.80  
  Purchase #6 $48.36   9.252%   $52.8343   $52.83   $52.85   $52.80  
  Purchase #7 $80.67   9.329%   $88.1957   $88.20   $88.20   $88.20  
  7 purchase totals = $830.27       $894.8028   $894.80   $894.80   $894.80