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 $186.65   7.681%   $200.9866   $200.99   $201.00   $201.00  
  Purchase #2 $84.28   12.717%   $94.9979   $95.00   $95.00   $95.00  
  Purchase #3 $35.52   4.680%   $37.1823   $37.18   $37.20   $37.20  
  Purchase #4 $57.83   3.594%   $59.9084   $59.91   $59.90   $59.90  
  Purchase #5 $165.27   8.116%   $178.6833   $178.68   $178.70   $178.70  
  Purchase #6 $106.75   12.296%   $119.876   $119.88   $119.90   $119.90  
  Purchase #7 $212.64   8.197%   $230.0701   $230.07   $230.05   $230.10  
  7 purchase totals = $848.94       $921.7046   $921.71   $921.75   $921.80