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 $107.32   11.507%   $119.6693   $119.67   $119.65   $119.70  
  Purchase #2 $233.40   10.735%   $258.4555   $258.46   $258.45   $258.50  
  Purchase #3 $50.90   11.168%   $56.5845   $56.58   $56.60   $56.60  
  Purchase #4 $146.65   10.232%   $161.6552   $161.66   $161.65   $161.70  
  Purchase #5 $64.44   4.459%   $67.3134   $67.31   $67.30   $67.30  
  Purchase #6 $204.72   10.249%   $225.7018   $225.70   $225.70   $225.70  
  Purchase #7 $31.51   7.395%   $33.8402   $33.84   $33.85   $33.80  
  7 purchase totals = $838.94       $923.2199   $923.22   $923.20   $923.30