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 $46.25   11.866%   $51.738   $51.74   $51.75   $51.70  
  Purchase #2 $5.27   7.648%   $5.673   $5.67   $5.65   $5.70  
  Purchase #3 $165.33   5.857%   $175.0134   $175.01   $175.00   $175.00  
  Purchase #4 $232.42   9.431%   $254.3395   $254.34   $254.35   $254.30  
  Purchase #5 $191.95   5.581%   $202.6627   $202.66   $202.65   $202.70  
  Purchase #6 $141.33   13.852%   $160.907   $160.91   $160.90   $160.90  
  Purchase #7 $155.69   5.407%   $164.1082   $164.11   $164.10   $164.10  
  7 purchase totals = $938.24       $1,014.4418   $1,014.44   $1,014.40   $1,014.40