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 $123.55   13.852%   $140.6641   $140.66   $140.65   $140.70  
  Purchase #2 $54.89   5.374%   $57.8398   $57.84   $57.85   $57.80  
  Purchase #3 $187.81   6.751%   $200.4891   $200.49   $200.50   $200.50  
  Purchase #4 $209.98   11.263%   $233.63   $233.63   $233.65   $233.60  
  Purchase #5 $114.97   5.449%   $121.2347   $121.23   $121.25   $121.20  
  Purchase #6 $57.54   11.541%   $64.1807   $64.18   $64.20   $64.20  
  Purchase #7 $182.98   11.510%   $204.041   $204.04   $204.05   $204.00  
  7 purchase totals = $931.72       $1,022.0794   $1,022.07   $1,022.15   $1,022.00