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 $165.76   10.188%   $182.6476   $182.65   $182.65   $182.60  
  Purchase #2 $139.87   7.505%   $150.3672   $150.37   $150.35   $150.40  
  Purchase #3 $17.52   6.532%   $18.6644   $18.66   $18.65   $18.70  
  Purchase #4 $78.84   8.776%   $85.759   $85.76   $85.75   $85.80  
  Purchase #5 $225.75   10.783%   $250.0926   $250.09   $250.10   $250.10  
  Purchase #6 $98.69   4.637%   $103.2663   $103.27   $103.25   $103.30  
  Purchase #7 $32.41   5.567%   $34.2143   $34.21   $34.20   $34.20  
  7 purchase totals = $758.84       $825.0114   $825.01   $824.95   $825.10