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 $211.74   6.714%   $225.9562   $225.96   $225.95   $226.00  
  Purchase #2 $129.40   3.290%   $133.6573   $133.66   $133.65   $133.70  
  Purchase #3 $104.50   4.355%   $109.051   $109.05   $109.05   $109.10  
  Purchase #4 $62.98   12.118%   $70.6119   $70.61   $70.60   $70.60  
  Purchase #5 $245.91   13.453%   $278.9923   $278.99   $279.00   $279.00  
  Purchase #6 $238.73   4.784%   $250.1508   $250.15   $250.15   $250.20  
  Purchase #7 $13.26   9.841%   $14.5649   $14.56   $14.55   $14.60  
  7 purchase totals = $1,006.52       $1,082.9844   $1,082.98   $1,082.95   $1,083.20