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 $226.86   12.295%   $254.7524   $254.75   $254.75   $254.80  
  Purchase #2 $24.58   8.403%   $26.6455   $26.65   $26.65   $26.60  
  Purchase #3 $78.80   6.581%   $83.9858   $83.99   $84.00   $84.00  
  Purchase #4 $62.35   8.237%   $67.4858   $67.49   $67.50   $67.50  
  Purchase #5 $232.53   13.444%   $263.7913   $263.79   $263.80   $263.80  
  Purchase #6 $61.81   9.399%   $67.6195   $67.62   $67.60   $67.60  
  Purchase #7 $183.73   4.310%   $191.6488   $191.65   $191.65   $191.60  
  7 purchase totals = $870.66       $955.9291   $955.94   $955.95   $955.90