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 $152.48   9.867%   $167.5252   $167.53   $167.55   $167.50  
  Purchase #2 $135.97   12.751%   $153.3075   $153.31   $153.30   $153.30  
  Purchase #3 $219.26   3.275%   $226.4408   $226.44   $226.45   $226.40  
  Purchase #4 $66.38   11.858%   $74.2513   $74.25   $74.25   $74.30  
  Purchase #5 $197.55   9.594%   $216.5029   $216.50   $216.50   $216.50  
  Purchase #6 $173.80   11.776%   $194.2667   $194.27   $194.25   $194.30  
  Purchase #7 $186.63   9.286%   $203.9605   $203.96   $203.95   $204.00  
  7 purchase totals = $1,132.07       $1,236.2549   $1,236.26   $1,236.25   $1,236.30