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 $242.49   9.552%   $265.6526   $265.65   $265.65   $265.70  
  Purchase #2 $62.76   11.363%   $69.8914   $69.89   $69.90   $69.90  
  Purchase #3 $197.56   4.254%   $205.9642   $205.96   $205.95   $206.00  
  Purchase #4 $205.55   6.446%   $218.7998   $218.80   $218.80   $218.80  
  Purchase #5 $138.46   11.632%   $154.5657   $154.57   $154.55   $154.60  
  Purchase #6 $198.39   10.453%   $219.1277   $219.13   $219.15   $219.10  
  Purchase #7 $92.48   10.594%   $102.2773   $102.28   $102.30   $102.30  
  7 purchase totals = $1,137.69       $1,236.2787   $1,236.28   $1,236.30   $1,236.40