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 $68.52   9.771%   $75.2151   $75.22   $75.20   $75.20  
  Purchase #2 $126.50   12.413%   $142.2024   $142.20   $142.20   $142.20  
  Purchase #3 $213.61   9.821%   $234.5886   $234.59   $234.60   $234.60  
  Purchase #4 $224.35   11.110%   $249.2753   $249.28   $249.30   $249.30  
  Purchase #5 $69.79   6.641%   $74.4248   $74.42   $74.40   $74.40  
  Purchase #6 $220.77   12.684%   $248.7725   $248.77   $248.75   $248.80  
  Purchase #7 $98.44   9.412%   $107.7052   $107.71   $107.70   $107.70  
  7 purchase totals = $1,021.98       $1,132.1839   $1,132.19   $1,132.15   $1,132.20