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 $191.42   11.220%   $212.8973   $212.90   $212.90   $212.90  
  Purchase #2 $244.94   13.364%   $277.6738   $277.67   $277.65   $277.70  
  Purchase #3 $41.67   11.111%   $46.3   $46.30   $46.30   $46.30  
  Purchase #4 $107.70   13.586%   $122.3321   $122.33   $122.35   $122.30  
  Purchase #5 $89.81   12.794%   $101.3003   $101.30   $101.30   $101.30  
  Purchase #6 $249.66   6.413%   $265.6707   $265.67   $265.65   $265.70  
  Purchase #7 $208.94   5.846%   $221.1546   $221.15   $221.15   $221.20  
  7 purchase totals = $1,134.14       $1,247.3288   $1,247.32   $1,247.30   $1,247.40