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 $111.45   6.812%   $119.042   $119.04   $119.05   $119.00  
  Purchase #2 $60.73   5.716%   $64.2013   $64.20   $64.20   $64.20  
  Purchase #3 $218.94   7.212%   $234.73   $234.73   $234.75   $234.70  
  Purchase #4 $170.44   6.379%   $181.3124   $181.31   $181.30   $181.30  
  Purchase #5 $85.46   3.578%   $88.5178   $88.52   $88.50   $88.50  
  Purchase #6 $205.97   11.586%   $229.8337   $229.83   $229.85   $229.80  
  Purchase #7 $30.43   6.125%   $32.2938   $32.29   $32.30   $32.30  
  7 purchase totals = $883.42       $949.9310   $949.92   $949.95   $949.80