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 $98.61   4.421%   $102.9695   $102.97   $102.95   $103.00  
  Purchase #2 $188.44   5.194%   $198.2276   $198.23   $198.25   $198.20  
  Purchase #3 $56.93   13.620%   $64.6839   $64.68   $64.70   $64.70  
  Purchase #4 $103.71   13.325%   $117.5294   $117.53   $117.55   $117.50  
  Purchase #5 $31.37   12.642%   $35.3358   $35.34   $35.35   $35.30  
  Purchase #6 $193.74   6.309%   $205.9631   $205.96   $205.95   $206.00  
  Purchase #7 $29.89   10.472%   $33.0201   $33.02   $33.00   $33.00  
  7 purchase totals = $702.69       $757.7294   $757.73   $757.75   $757.70