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 $194.41   5.856%   $205.7946   $205.79   $205.80   $205.80  
  Purchase #2 $118.43   11.148%   $131.6326   $131.63   $131.65   $131.60  
  Purchase #3 $200.31   9.652%   $219.6439   $219.64   $219.65   $219.60  
  Purchase #4 $98.54   12.709%   $111.0634   $111.06   $111.05   $111.10  
  Purchase #5 $138.96   7.604%   $149.5265   $149.53   $149.55   $149.50  
  Purchase #6 $203.87   8.376%   $220.9462   $220.95   $220.95   $220.90  
  Purchase #7 $211.63   11.591%   $236.16   $236.16   $236.15   $236.20  
  7 purchase totals = $1,166.15       $1,274.7672   $1,274.76   $1,274.80   $1,274.70