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 $65.64   11.210%   $72.9982   $73.00   $73.00   $73.00  
  Purchase #2 $148.75   11.342%   $165.6212   $165.62   $165.60   $165.60  
  Purchase #3 $168.76   7.807%   $181.9351   $181.94   $181.95   $181.90  
  Purchase #4 $122.98   3.817%   $127.6741   $127.67   $127.65   $127.70  
  Purchase #5 $120.27   10.837%   $133.3037   $133.30   $133.30   $133.30  
  Purchase #6 $233.26   11.540%   $260.1782   $260.18   $260.20   $260.20  
  Purchase #7 $33.38   4.738%   $34.9615   $34.96   $34.95   $35.00  
  7 purchase totals = $893.04       $976.6720   $976.67   $976.65   $976.70