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 $24.66   6.531%   $26.2705   $26.27   $26.25   $26.30  
  Purchase #2 $238.94   10.157%   $263.2091   $263.21   $263.20   $263.20  
  Purchase #3 $81.64   8.258%   $88.3818   $88.38   $88.40   $88.40  
  Purchase #4 $102.86   6.181%   $109.2178   $109.22   $109.20   $109.20  
  Purchase #5 $173.46   12.392%   $194.9552   $194.96   $194.95   $195.00  
  Purchase #6 $71.34   12.653%   $80.3667   $80.37   $80.35   $80.40  
  Purchase #7 $25.37   3.433%   $26.241   $26.24   $26.25   $26.20  
  7 purchase totals = $718.27       $788.6421   $788.65   $788.60   $788.70