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 $47.89   11.192%   $53.2498   $53.25   $53.25   $53.20  
  Purchase #2 $55.62   4.853%   $58.3192   $58.32   $58.30   $58.30  
  Purchase #3 $204.70   9.431%   $224.0053   $224.01   $224.00   $224.00  
  Purchase #4 $229.41   10.874%   $254.356   $254.36   $254.35   $254.40  
  Purchase #5 $149.66   12.643%   $168.5815   $168.58   $168.60   $168.60  
  Purchase #6 $163.45   11.495%   $182.2386   $182.24   $182.25   $182.20  
  Purchase #7 $120.56   8.272%   $130.5327   $130.53   $130.55   $130.50  
  7 purchase totals = $971.29       $1,071.2831   $1,071.29   $1,071.30   $1,071.20