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 $57.71   9.585%   $63.2415   $63.24   $63.25   $63.20  
  Purchase #2 $241.27   5.322%   $254.1104   $254.11   $254.10   $254.10  
  Purchase #3 $154.88   7.637%   $166.7082   $166.71   $166.70   $166.70  
  Purchase #4 $165.79   8.716%   $180.2403   $180.24   $180.25   $180.20  
  Purchase #5 $213.71   12.419%   $240.2506   $240.25   $240.25   $240.30  
  Purchase #6 $120.92   4.195%   $125.9926   $125.99   $126.00   $126.00  
  Purchase #7 $250.68   11.799%   $280.2577   $280.26   $280.25   $280.30  
  7 purchase totals = $1,204.96       $1,310.8013   $1,310.80   $1,310.80   $1,310.80