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 $54.46   13.551%   $61.8399   $61.84   $61.85   $61.80  
  Purchase #2 $224.84   12.651%   $253.2845   $253.28   $253.30   $253.30  
  Purchase #3 $175.83   11.169%   $195.4685   $195.47   $195.45   $195.50  
  Purchase #4 $85.81   8.222%   $92.8653   $92.87   $92.85   $92.90  
  Purchase #5 $88.65   6.256%   $94.1959   $94.20   $94.20   $94.20  
  Purchase #6 $96.58   11.719%   $107.8982   $107.90   $107.90   $107.90  
  Purchase #7 $97.39   9.829%   $106.9625   $106.96   $106.95   $107.00  
  7 purchase totals = $823.56       $912.5148   $912.52   $912.50   $912.60