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 $207.50   12.129%   $232.6677   $232.67   $232.65   $232.70  
  Purchase #2 $105.27   11.486%   $117.3613   $117.36   $117.35   $117.40  
  Purchase #3 $174.88   5.107%   $183.8111   $183.81   $183.80   $183.80  
  Purchase #4 $45.29   6.423%   $48.199   $48.20   $48.20   $48.20  
  Purchase #5 $119.55   13.772%   $136.0144   $136.01   $136.00   $136.00  
  Purchase #6 $220.42   6.259%   $234.2161   $234.22   $234.20   $234.20  
  Purchase #7 $12.39   11.710%   $13.8409   $13.84   $13.85   $13.80  
  7 purchase totals = $885.30       $966.1105   $966.11   $966.05   $966.10