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 $167.89   6.624%   $179.011   $179.01   $179.00   $179.00  
  Purchase #2 $12.98   10.317%   $14.3191   $14.32   $14.30   $14.30  
  Purchase #3 $13.28   5.553%   $14.0174   $14.02   $14.00   $14.00  
  Purchase #4 $192.87   5.268%   $203.0304   $203.03   $203.05   $203.00  
  Purchase #5 $121.71   7.461%   $130.7908   $130.79   $130.80   $130.80  
  Purchase #6 $202.42   5.546%   $213.6462   $213.65   $213.65   $213.60  
  Purchase #7 $70.93   7.607%   $76.3256   $76.33   $76.35   $76.30  
  7 purchase totals = $782.08       $831.1405   $831.15   $831.15   $831.00