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 $47.47   13.674%   $53.961   $53.96   $53.95   $54.00  
  Purchase #2 $190.75   12.333%   $214.2752   $214.28   $214.30   $214.30  
  Purchase #3 $248.78   10.258%   $274.2999   $274.30   $274.30   $274.30  
  Purchase #4 $74.77   12.707%   $84.271   $84.27   $84.25   $84.30  
  Purchase #5 $205.31   7.571%   $220.854   $220.85   $220.85   $220.90  
  Purchase #6 $37.32   12.532%   $41.9969   $42.00   $42.00   $42.00  
  Purchase #7 $165.35   3.130%   $170.5255   $170.53   $170.55   $170.50  
  7 purchase totals = $969.75       $1,060.1835   $1,060.19   $1,060.20   $1,060.30