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 $92.80   4.344%   $96.8312   $96.83   $96.85   $96.80  
  Purchase #2 $246.79   7.492%   $265.2795   $265.28   $265.30   $265.30  
  Purchase #3 $224.66   10.586%   $248.4425   $248.44   $248.45   $248.40  
  Purchase #4 $85.96   10.331%   $94.8405   $94.84   $94.85   $94.80  
  Purchase #5 $187.49   9.755%   $205.7796   $205.78   $205.80   $205.80  
  Purchase #6 $44.46   6.849%   $47.5051   $47.51   $47.50   $47.50  
  Purchase #7 $51.52   11.674%   $57.5344   $57.53   $57.55   $57.50  
  7 purchase totals = $933.68       $1,016.2128   $1,016.21   $1,016.30   $1,016.10