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 $41.46   7.547%   $44.589   $44.59   $44.60   $44.60  
  Purchase #2 $51.41   9.334%   $56.2086   $56.21   $56.20   $56.20  
  Purchase #3 $197.33   8.712%   $214.5214   $214.52   $214.50   $214.50  
  Purchase #4 $65.44   13.137%   $74.0369   $74.04   $74.05   $74.00  
  Purchase #5 $65.35   11.408%   $72.8051   $72.81   $72.80   $72.80  
  Purchase #6 $165.80   5.275%   $174.546   $174.55   $174.55   $174.50  
  Purchase #7 $81.26   13.657%   $92.3577   $92.36   $92.35   $92.40  
  7 purchase totals = $668.05       $729.0647   $729.08   $729.05   $729.00