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 $57.74   5.303%   $60.802   $60.80   $60.80   $60.80  
  Purchase #2 $66.44   3.352%   $68.6671   $68.67   $68.65   $68.70  
  Purchase #3 $107.79   6.288%   $114.5678   $114.57   $114.55   $114.60  
  Purchase #4 $232.79   4.642%   $243.5961   $243.60   $243.60   $243.60  
  Purchase #5 $130.29   9.525%   $142.7001   $142.70   $142.70   $142.70  
  Purchase #6 $46.57   5.707%   $49.2277   $49.23   $49.25   $49.20  
  Purchase #7 $183.27   12.579%   $206.3235   $206.32   $206.30   $206.30  
  7 purchase totals = $824.89       $885.8843   $885.89   $885.85   $885.90