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 $48.47   11.470%   $54.0295   $54.03   $54.05   $54.00  
  Purchase #2 $173.54   11.741%   $193.9153   $193.92   $193.90   $193.90  
  Purchase #3 $85.34   9.700%   $93.618   $93.62   $93.60   $93.60  
  Purchase #4 $213.60   9.593%   $234.0906   $234.09   $234.10   $234.10  
  Purchase #5 $248.90   8.371%   $269.7354   $269.74   $269.75   $269.70  
  Purchase #6 $199.70   6.154%   $211.9895   $211.99   $212.00   $212.00  
  Purchase #7 $159.46   11.334%   $177.5332   $177.53   $177.55   $177.50  
  7 purchase totals = $1,129.01       $1,234.9115   $1,234.92   $1,234.95   $1,234.80