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 $71.71   5.796%   $75.8663   $75.87   $75.85   $75.90  
  Purchase #2 $241.30   10.365%   $266.3107   $266.31   $266.30   $266.30  
  Purchase #3 $70.92   6.802%   $75.744   $75.74   $75.75   $75.70  
  Purchase #4 $200.68   11.342%   $223.4411   $223.44   $223.45   $223.40  
  Purchase #5 $48.28   7.737%   $52.0154   $52.02   $52.00   $52.00  
  Purchase #6 $223.42   6.519%   $237.9847   $237.98   $238.00   $238.00  
  Purchase #7 $228.90   8.729%   $248.8807   $248.88   $248.90   $248.90  
  7 purchase totals = $1,085.21       $1,180.2429   $1,180.24   $1,180.25   $1,180.20