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 $208.49   8.496%   $226.2033   $226.20   $226.20   $226.20  
  Purchase #2 $33.31   10.660%   $36.8608   $36.86   $36.85   $36.90  
  Purchase #3 $237.29   11.383%   $264.3007   $264.30   $264.30   $264.30  
  Purchase #4 $183.75   9.810%   $201.7759   $201.78   $201.80   $201.80  
  Purchase #5 $83.79   10.516%   $92.6014   $92.60   $92.60   $92.60  
  Purchase #6 $230.89   7.638%   $248.5254   $248.53   $248.55   $248.50  
  Purchase #7 $239.25   7.489%   $257.1674   $257.17   $257.15   $257.20  
  7 purchase totals = $1,216.77       $1,327.4349   $1,327.44   $1,327.45   $1,327.50