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 $220.75   11.674%   $246.5204   $246.52   $246.50   $246.50  
  Purchase #2 $97.94   13.691%   $111.349   $111.35   $111.35   $111.30  
  Purchase #3 $25.41   12.428%   $28.568   $28.57   $28.55   $28.60  
  Purchase #4 $115.53   12.655%   $130.1503   $130.15   $130.15   $130.20  
  Purchase #5 $191.67   7.219%   $205.5067   $205.51   $205.50   $205.50  
  Purchase #6 $205.90   7.172%   $220.6671   $220.67   $220.65   $220.70  
  Purchase #7 $246.77   6.813%   $263.5824   $263.58   $263.60   $263.60  
  7 purchase totals = $1,103.97       $1,206.3439   $1,206.35   $1,206.30   $1,206.40