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 $86.68   13.798%   $98.6401   $98.64   $98.65   $98.60  
  Purchase #2 $234.69   12.829%   $264.7984   $264.80   $264.80   $264.80  
  Purchase #3 $142.71   4.336%   $148.8979   $148.90   $148.90   $148.90  
  Purchase #4 $107.57   10.174%   $118.5142   $118.51   $118.50   $118.50  
  Purchase #5 $196.75   8.300%   $213.0803   $213.08   $213.10   $213.10  
  Purchase #6 $243.73   9.652%   $267.2548   $267.25   $267.25   $267.30  
  Purchase #7 $181.49   5.761%   $191.9456   $191.95   $191.95   $191.90  
  7 purchase totals = $1,193.62       $1,303.1313   $1,303.13   $1,303.15   $1,303.10