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 $69.99   9.773%   $76.8301   $76.83   $76.85   $76.80  
  Purchase #2 $141.25   6.181%   $149.9807   $149.98   $150.00   $150.00  
  Purchase #3 $107.65   6.298%   $114.4298   $114.43   $114.45   $114.40  
  Purchase #4 $62.29   10.132%   $68.6012   $68.60   $68.60   $68.60  
  Purchase #5 $178.55   4.719%   $186.9758   $186.98   $187.00   $187.00  
  Purchase #6 $6.93   9.413%   $7.5823   $7.58   $7.60   $7.60  
  Purchase #7 $95.72   7.733%   $103.122   $103.12   $103.10   $103.10  
  7 purchase totals = $662.38       $707.5219   $707.52   $707.60   $707.50