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 $10.54   12.299%   $11.8363   $11.84   $11.85   $11.80  
  Purchase #2 $159.61   8.594%   $173.3269   $173.33   $173.35   $173.30  
  Purchase #3 $117.40   6.427%   $124.9453   $124.95   $124.95   $124.90  
  Purchase #4 $237.66   4.754%   $248.9584   $248.96   $248.95   $249.00  
  Purchase #5 $213.96   9.151%   $233.5395   $233.54   $233.55   $233.50  
  Purchase #6 $184.26   8.548%   $200.0105   $200.01   $200.00   $200.00  
  Purchase #7 $235.31   12.508%   $264.7426   $264.74   $264.75   $264.70  
  7 purchase totals = $1,158.74       $1,257.3595   $1,257.37   $1,257.40   $1,257.20