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 $235.49   6.767%   $251.4256   $251.43   $251.45   $251.40  
  Purchase #2 $168.98   3.426%   $174.7693   $174.77   $174.75   $174.80  
  Purchase #3 $88.83   8.666%   $96.528   $96.53   $96.55   $96.50  
  Purchase #4 $65.74   7.235%   $70.4963   $70.50   $70.50   $70.50  
  Purchase #5 $204.81   6.683%   $218.4975   $218.50   $218.50   $218.50  
  Purchase #6 $69.37   3.359%   $71.7001   $71.70   $71.70   $71.70  
  Purchase #7 $84.37   10.858%   $93.5309   $93.53   $93.55   $93.50  
  7 purchase totals = $917.59       $976.9477   $976.96   $977.00   $976.90