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 $206.75   13.420%   $234.4959   $234.50   $234.50   $234.50  
  Purchase #2 $165.96   9.277%   $181.3561   $181.36   $181.35   $181.40  
  Purchase #3 $221.37   7.564%   $238.1144   $238.11   $238.10   $238.10  
  Purchase #4 $75.31   6.725%   $80.3746   $80.37   $80.35   $80.40  
  Purchase #5 $202.54   13.791%   $230.4723   $230.47   $230.45   $230.50  
  Purchase #6 $221.86   8.401%   $240.4985   $240.50   $240.50   $240.50  
  Purchase #7 $119.25   6.308%   $126.7723   $126.77   $126.75   $126.80  
  7 purchase totals = $1,213.04       $1,332.0841   $1,332.08   $1,332.00   $1,332.20