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 $61.49   13.160%   $69.5821   $69.58   $69.60   $69.60  
  Purchase #2 $83.58   6.295%   $88.8414   $88.84   $88.85   $88.80  
  Purchase #3 $246.89   9.753%   $270.9692   $270.97   $270.95   $271.00  
  Purchase #4 $172.42   7.738%   $185.7619   $185.76   $185.75   $185.80  
  Purchase #5 $112.62   6.662%   $120.1227   $120.12   $120.10   $120.10  
  Purchase #6 $158.32   3.484%   $163.8359   $163.84   $163.85   $163.80  
  Purchase #7 $211.34   6.393%   $224.851   $224.85   $224.85   $224.90  
  7 purchase totals = $1,046.66       $1,123.9642   $1,123.96   $1,123.95   $1,124.00