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 $50.71   6.296%   $53.9027   $53.90   $53.90   $53.90  
  Purchase #2 $233.95   11.480%   $260.8075   $260.81   $260.80   $260.80  
  Purchase #3 $189.37   7.703%   $203.9572   $203.96   $203.95   $204.00  
  Purchase #4 $94.58   11.223%   $105.1947   $105.19   $105.20   $105.20  
  Purchase #5 $58.38   12.494%   $65.674   $65.67   $65.65   $65.70  
  Purchase #6 $232.45   7.325%   $249.477   $249.48   $249.50   $249.50  
  Purchase #7 $107.57   3.670%   $111.5178   $111.52   $111.50   $111.50  
  7 purchase totals = $967.01       $1,050.5309   $1,050.53   $1,050.50   $1,050.60