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 $105.42   13.231%   $119.3681   $119.37   $119.35   $119.40  
  Purchase #2 $55.89   9.593%   $61.2515   $61.25   $61.25   $61.30  
  Purchase #3 $182.99   6.174%   $194.2878   $194.29   $194.30   $194.30  
  Purchase #4 $147.57   7.502%   $158.6407   $158.64   $158.65   $158.60  
  Purchase #5 $108.76   7.374%   $116.78   $116.78   $116.80   $116.80  
  Purchase #6 $184.38   11.717%   $205.9838   $205.98   $206.00   $206.00  
  Purchase #7 $246.60   7.874%   $266.0173   $266.02   $266.00   $266.00  
  7 purchase totals = $1,031.61       $1,122.3292   $1,122.33   $1,122.35   $1,122.40