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 $213.39   13.464%   $242.1208   $242.12   $242.10   $242.10  
  Purchase #2 $247.31   8.167%   $267.5078   $267.51   $267.50   $267.50  
  Purchase #3 $249.51   12.759%   $281.345   $281.35   $281.35   $281.30  
  Purchase #4 $32.41   7.117%   $34.7166   $34.72   $34.70   $34.70  
  Purchase #5 $244.48   13.316%   $277.035   $277.04   $277.05   $277.00  
  Purchase #6 $44.51   7.564%   $47.8767   $47.88   $47.90   $47.90  
  Purchase #7 $86.81   7.865%   $93.6376   $93.64   $93.65   $93.60  
  7 purchase totals = $1,118.42       $1,244.2395   $1,244.26   $1,244.25   $1,244.10