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 $246.53   10.142%   $271.5331   $271.53   $271.55   $271.50  
  Purchase #2 $219.39   9.529%   $240.2957   $240.30   $240.30   $240.30  
  Purchase #3 $219.64   4.286%   $229.0538   $229.05   $229.05   $229.10  
  Purchase #4 $214.56   4.209%   $223.5908   $223.59   $223.60   $223.60  
  Purchase #5 $47.35   12.510%   $53.2735   $53.27   $53.25   $53.30  
  Purchase #6 $201.30   6.494%   $214.3724   $214.37   $214.35   $214.40  
  Purchase #7 $18.89   7.402%   $20.2882   $20.29   $20.30   $20.30  
  7 purchase totals = $1,167.66       $1,252.4075   $1,252.40   $1,252.40   $1,252.50