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 $249.50   7.185%   $267.4266   $267.43   $267.45   $267.40  
  Purchase #2 $93.51   8.410%   $101.3742   $101.37   $101.35   $101.40  
  Purchase #3 $166.90   13.112%   $188.7839   $188.78   $188.80   $188.80  
  Purchase #4 $131.45   5.248%   $138.3485   $138.35   $138.35   $138.30  
  Purchase #5 $97.55   13.191%   $110.4178   $110.42   $110.40   $110.40  
  Purchase #6 $94.62   13.384%   $107.2839   $107.28   $107.30   $107.30  
  Purchase #7 $177.92   4.103%   $185.2201   $185.22   $185.20   $185.20  
  7 purchase totals = $1,011.45       $1,098.8550   $1,098.85   $1,098.85   $1,098.80