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 $88.26   8.571%   $95.8248   $95.82   $95.80   $95.80  
  Purchase #2 $134.72   11.772%   $150.5792   $150.58   $150.60   $150.60  
  Purchase #3 $10.90   11.681%   $12.1732   $12.17   $12.15   $12.20  
  Purchase #4 $118.92   8.801%   $129.3861   $129.39   $129.40   $129.40  
  Purchase #5 $153.38   4.621%   $160.4677   $160.47   $160.45   $160.50  
  Purchase #6 $240.96   3.132%   $248.5069   $248.51   $248.50   $248.50  
  Purchase #7 $207.97   4.256%   $216.8212   $216.82   $216.80   $216.80  
  7 purchase totals = $955.11       $1,013.7591   $1,013.76   $1,013.70   $1,013.80