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 $156.47   3.244%   $161.5459   $161.55   $161.55   $161.50  
  Purchase #2 $148.53   7.121%   $159.1068   $159.11   $159.10   $159.10  
  Purchase #3 $215.46   9.580%   $236.1011   $236.10   $236.10   $236.10  
  Purchase #4 $39.65   3.573%   $41.0667   $41.07   $41.05   $41.10  
  Purchase #5 $185.34   4.488%   $193.6581   $193.66   $193.65   $193.70  
  Purchase #6 $131.45   8.822%   $143.0465   $143.05   $143.05   $143.00  
  Purchase #7 $80.73   9.635%   $88.5083   $88.51   $88.50   $88.50  
  7 purchase totals = $957.63       $1,023.0334   $1,023.05   $1,023.00   $1,023.00