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 $250.32   4.782%   $262.2903   $262.29   $262.30   $262.30  
  Purchase #2 $80.49   9.187%   $87.8846   $87.88   $87.90   $87.90  
  Purchase #3 $125.52   8.539%   $136.2382   $136.24   $136.25   $136.20  
  Purchase #4 $100.66   6.554%   $107.2573   $107.26   $107.25   $107.30  
  Purchase #5 $209.41   7.534%   $225.1869   $225.19   $225.20   $225.20  
  Purchase #6 $128.76   9.708%   $141.26   $141.26   $141.25   $141.30  
  Purchase #7 $8.67   12.666%   $9.7681   $9.77   $9.75   $9.80  
  7 purchase totals = $903.83       $969.8854   $969.89   $969.90   $970.00