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 $87.28   12.494%   $98.1848   $98.18   $98.20   $98.20  
  Purchase #2 $127.43   7.304%   $136.7375   $136.74   $136.75   $136.70  
  Purchase #3 $202.40   11.439%   $225.5525   $225.55   $225.55   $225.60  
  Purchase #4 $185.35   4.787%   $194.2227   $194.22   $194.20   $194.20  
  Purchase #5 $243.40   7.580%   $261.8497   $261.85   $261.85   $261.80  
  Purchase #6 $194.74   5.338%   $205.1352   $205.14   $205.15   $205.10  
  Purchase #7 $223.64   7.190%   $239.7197   $239.72   $239.70   $239.70  
  7 purchase totals = $1,264.24       $1,361.4021   $1,361.40   $1,361.40   $1,361.30