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 $201.31   8.507%   $218.4354   $218.44   $218.45   $218.40  
  Purchase #2 $124.94   4.169%   $130.1487   $130.15   $130.15   $130.10  
  Purchase #3 $46.83   11.715%   $52.3161   $52.32   $52.30   $52.30  
  Purchase #4 $42.80   8.870%   $46.5964   $46.60   $46.60   $46.60  
  Purchase #5 $237.36   11.586%   $264.8605   $264.86   $264.85   $264.90  
  Purchase #6 $64.87   4.825%   $68   $68.00   $68.00   $68.00  
  Purchase #7 $162.33   7.298%   $174.1768   $174.18   $174.20   $174.20  
  7 purchase totals = $880.44       $954.5339   $954.55   $954.55   $954.50