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 $65.41   8.562%   $71.0104   $71.01   $71.00   $71.00  
  Purchase #2 $142.73   10.523%   $157.7495   $157.75   $157.75   $157.70  
  Purchase #3 $165.79   9.488%   $181.5202   $181.52   $181.50   $181.50  
  Purchase #4 $41.27   9.798%   $45.3136   $45.31   $45.30   $45.30  
  Purchase #5 $21.83   13.634%   $24.8063   $24.81   $24.80   $24.80  
  Purchase #6 $206.91   11.316%   $230.3239   $230.32   $230.30   $230.30  
  Purchase #7 $240.26   9.548%   $263.2   $263.20   $263.20   $263.20  
  7 purchase totals = $884.20       $973.9239   $973.92   $973.85   $973.80