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 $146.76   4.764%   $153.7516   $153.75   $153.75   $153.80  
  Purchase #2 $224.66   6.389%   $239.0135   $239.01   $239.00   $239.00  
  Purchase #3 $114.27   6.580%   $121.789   $121.79   $121.80   $121.80  
  Purchase #4 $102.62   3.650%   $106.3656   $106.37   $106.35   $106.40  
  Purchase #5 $103.53   13.113%   $117.1059   $117.11   $117.10   $117.10  
  Purchase #6 $233.90   5.539%   $246.8557   $246.86   $246.85   $246.90  
  Purchase #7 $19.56   6.188%   $20.7704   $20.77   $20.75   $20.80  
  7 purchase totals = $945.30       $1,005.6517   $1,005.66   $1,005.60   $1,005.80