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 $213.63   8.740%   $232.3013   $232.30   $232.30   $232.30  
  Purchase #2 $196.51   9.394%   $214.9701   $214.97   $214.95   $215.00  
  Purchase #3 $167.36   8.108%   $180.9295   $180.93   $180.95   $180.90  
  Purchase #4 $128.25   4.402%   $133.8956   $133.90   $133.90   $133.90  
  Purchase #5 $169.62   12.755%   $191.255   $191.26   $191.25   $191.30  
  Purchase #6 $90.48   4.394%   $94.4557   $94.46   $94.45   $94.50  
  Purchase #7 $213.36   11.547%   $237.9967   $238.00   $238.00   $238.00  
  7 purchase totals = $1,179.21       $1,285.8039   $1,285.82   $1,285.80   $1,285.90