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 $197.42   7.340%   $211.9106   $211.91   $211.90   $211.90  
  Purchase #2 $250.74   9.499%   $274.5578   $274.56   $274.55   $274.60  
  Purchase #3 $6.49   8.407%   $7.0356   $7.04   $7.05   $7.00  
  Purchase #4 $113.55   4.215%   $118.3361   $118.34   $118.35   $118.30  
  Purchase #5 $81.76   4.735%   $85.6313   $85.63   $85.65   $85.60  
  Purchase #6 $148.88   7.340%   $159.8078   $159.81   $159.80   $159.80  
  Purchase #7 $155.83   13.689%   $177.1616   $177.16   $177.15   $177.20  
  7 purchase totals = $954.67       $1,034.4408   $1,034.45   $1,034.45   $1,034.40