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 $153.56   7.317%   $164.796   $164.80   $164.80   $164.80  
  Purchase #2 $219.35   7.583%   $235.9833   $235.98   $236.00   $236.00  
  Purchase #3 $19.96   12.628%   $22.4805   $22.48   $22.50   $22.50  
  Purchase #4 $185.58   4.822%   $194.5287   $194.53   $194.55   $194.50  
  Purchase #5 $196.49   4.528%   $205.3871   $205.39   $205.40   $205.40  
  Purchase #6 $225.42   10.130%   $248.255   $248.26   $248.25   $248.30  
  Purchase #7 $70.76   6.182%   $75.1344   $75.13   $75.15   $75.10  
  7 purchase totals = $1,071.12       $1,146.5650   $1,146.57   $1,146.65   $1,146.60