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 $215.58   8.123%   $233.0916   $233.09   $233.10   $233.10  
  Purchase #2 $213.76   12.818%   $241.1598   $241.16   $241.15   $241.20  
  Purchase #3 $46.44   6.536%   $49.4753   $49.48   $49.50   $49.50  
  Purchase #4 $185.34   13.823%   $210.9595   $210.96   $210.95   $211.00  
  Purchase #5 $103.29   5.341%   $108.8067   $108.81   $108.80   $108.80  
  Purchase #6 $146.40   9.196%   $159.8629   $159.86   $159.85   $159.90  
  Purchase #7 $82.44   10.360%   $90.9808   $90.98   $91.00   $91.00  
  7 purchase totals = $993.25       $1,094.3366   $1,094.34   $1,094.35   $1,094.50