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 $226.57   11.124%   $251.7736   $251.77   $251.75   $251.80  
  Purchase #2 $48.45   4.247%   $50.5077   $50.51   $50.50   $50.50  
  Purchase #3 $185.51   6.715%   $197.967   $197.97   $197.95   $198.00  
  Purchase #4 $194.83   10.466%   $215.2209   $215.22   $215.20   $215.20  
  Purchase #5 $199.50   10.236%   $219.9208   $219.92   $219.90   $219.90  
  Purchase #6 $55.60   5.157%   $58.4673   $58.47   $58.45   $58.50  
  Purchase #7 $53.87   4.781%   $56.4455   $56.45   $56.45   $56.40  
  7 purchase totals = $964.33       $1,050.3028   $1,050.31   $1,050.20   $1,050.30