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 $57.26   4.748%   $59.9787   $59.98   $60.00   $60.00  
  Purchase #2 $233.92   6.287%   $248.6266   $248.63   $248.65   $248.60  
  Purchase #3 $242.86   12.497%   $273.2102   $273.21   $273.20   $273.20  
  Purchase #4 $36.63   12.599%   $41.245   $41.25   $41.25   $41.20  
  Purchase #5 $189.40   6.751%   $202.1864   $202.19   $202.20   $202.20  
  Purchase #6 $75.65   8.338%   $81.9577   $81.96   $81.95   $82.00  
  Purchase #7 $118.30   10.712%   $130.9723   $130.97   $130.95   $131.00  
  7 purchase totals = $954.02       $1,038.1769   $1,038.19   $1,038.20   $1,038.20