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 $188.76   9.817%   $207.2906   $207.29   $207.30   $207.30  
  Purchase #2 $161.78   11.793%   $180.8587   $180.86   $180.85   $180.90  
  Purchase #3 $162.44   8.464%   $176.1889   $176.19   $176.20   $176.20  
  Purchase #4 $32.68   8.124%   $35.3349   $35.33   $35.35   $35.30  
  Purchase #5 $59.94   13.367%   $67.9522   $67.95   $67.95   $68.00  
  Purchase #6 $238.96   4.700%   $250.1911   $250.19   $250.20   $250.20  
  Purchase #7 $134.76   8.633%   $146.3938   $146.39   $146.40   $146.40  
  7 purchase totals = $979.32       $1,064.2102   $1,064.20   $1,064.25   $1,064.30