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 $206.99   13.356%   $234.6356   $234.64   $234.65   $234.60  
  Purchase #2 $131.50   10.648%   $145.5021   $145.50   $145.50   $145.50  
  Purchase #3 $121.28   9.368%   $132.6415   $132.64   $132.65   $132.60  
  Purchase #4 $215.28   10.590%   $238.0782   $238.08   $238.10   $238.10  
  Purchase #5 $86.78   7.714%   $93.4742   $93.47   $93.45   $93.50  
  Purchase #6 $81.74   3.122%   $84.2919   $84.29   $84.30   $84.30  
  Purchase #7 $126.47   5.308%   $133.183   $133.18   $133.20   $133.20  
  7 purchase totals = $970.04       $1,061.8065   $1,061.80   $1,061.85   $1,061.80