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 $48.72   7.307%   $52.28   $52.28   $52.30   $52.30  
  Purchase #2 $81.85   8.110%   $88.488   $88.49   $88.50   $88.50  
  Purchase #3 $165.33   5.309%   $174.1074   $174.11   $174.10   $174.10  
  Purchase #4 $212.58   6.441%   $226.2723   $226.27   $226.25   $226.30  
  Purchase #5 $69.61   8.289%   $75.38   $75.38   $75.40   $75.40  
  Purchase #6 $24.50   3.802%   $25.4315   $25.43   $25.45   $25.40  
  Purchase #7 $177.32   10.435%   $195.8233   $195.82   $195.80   $195.80  
  7 purchase totals = $779.91       $837.7825   $837.78   $837.80   $837.80