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 $86.52   10.190%   $95.3364   $95.34   $95.35   $95.30  
  Purchase #2 $111.82   6.183%   $118.7338   $118.73   $118.75   $118.70  
  Purchase #3 $148.32   9.145%   $161.8839   $161.88   $161.90   $161.90  
  Purchase #4 $148.99   12.805%   $168.0682   $168.07   $168.05   $168.10  
  Purchase #5 $124.59   4.842%   $130.6226   $130.62   $130.60   $130.60  
  Purchase #6 $90.74   11.686%   $101.3439   $101.34   $101.35   $101.30  
  Purchase #7 $106.52   10.442%   $117.6428   $117.64   $117.65   $117.60  
  7 purchase totals = $817.50       $893.6316   $893.62   $893.65   $893.50