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 $181.35   13.578%   $205.9737   $205.97   $205.95   $206.00  
  Purchase #2 $134.46   10.658%   $148.7907   $148.79   $148.80   $148.80  
  Purchase #3 $204.25   3.106%   $210.594   $210.59   $210.60   $210.60  
  Purchase #4 $207.53   4.536%   $216.9436   $216.94   $216.95   $216.90  
  Purchase #5 $42.51   6.562%   $45.2995   $45.30   $45.30   $45.30  
  Purchase #6 $161.98   9.425%   $177.2466   $177.25   $177.25   $177.20  
  Purchase #7 $185.64   4.693%   $194.3521   $194.35   $194.35   $194.40  
  7 purchase totals = $1,117.72       $1,199.2002   $1,199.19   $1,199.20   $1,199.20