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 $89.68   5.560%   $94.6662   $94.67   $94.65   $94.70  
  Purchase #2 $214.80   13.113%   $242.9667   $242.97   $242.95   $243.00  
  Purchase #3 $234.48   13.739%   $266.6952   $266.70   $266.70   $266.70  
  Purchase #4 $175.70   4.421%   $183.4677   $183.47   $183.45   $183.50  
  Purchase #5 $102.78   4.118%   $107.0125   $107.01   $107.00   $107.00  
  Purchase #6 $234.92   5.254%   $247.2627   $247.26   $247.25   $247.30  
  Purchase #7 $205.98   11.105%   $228.8541   $228.85   $228.85   $228.90  
  7 purchase totals = $1,258.34       $1,370.9251   $1,370.93   $1,370.85   $1,371.10