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 $138.53   9.557%   $151.7693   $151.77   $151.75   $151.80  
  Purchase #2 $73.43   3.840%   $76.2497   $76.25   $76.25   $76.20  
  Purchase #3 $88.59   10.594%   $97.9752   $97.98   $98.00   $98.00  
  Purchase #4 $234.59   5.183%   $246.7488   $246.75   $246.75   $246.70  
  Purchase #5 $184.85   11.206%   $205.5643   $205.56   $205.55   $205.60  
  Purchase #6 $77.91   9.546%   $85.3473   $85.35   $85.35   $85.30  
  Purchase #7 $191.64   3.136%   $197.6498   $197.65   $197.65   $197.60  
  7 purchase totals = $989.54       $1,061.3044   $1,061.31   $1,061.30   $1,061.20