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 $164.60   13.294%   $186.4819   $186.48   $186.50   $186.50  
  Purchase #2 $212.89   9.325%   $232.742   $232.74   $232.75   $232.70  
  Purchase #3 $61.97   7.712%   $66.7491   $66.75   $66.75   $66.70  
  Purchase #4 $164.45   7.422%   $176.6555   $176.66   $176.65   $176.70  
  Purchase #5 $41.82   11.589%   $46.6665   $46.67   $46.65   $46.70  
  Purchase #6 $57.77   11.641%   $64.495   $64.50   $64.50   $64.50  
  Purchase #7 $30.31   10.585%   $33.5183   $33.52   $33.50   $33.50  
  7 purchase totals = $733.81       $807.3083   $807.32   $807.30   $807.30