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 $57.70   10.347%   $63.6702   $63.67   $63.65   $63.70  
  Purchase #2 $130.96   13.523%   $148.6697   $148.67   $148.65   $148.70  
  Purchase #3 $23.65   6.744%   $25.245   $25.25   $25.25   $25.20  
  Purchase #4 $204.83   7.873%   $220.9563   $220.96   $220.95   $221.00  
  Purchase #5 $157.59   6.670%   $168.1013   $168.10   $168.10   $168.10  
  Purchase #6 $116.45   6.289%   $123.7735   $123.77   $123.75   $123.80  
  Purchase #7 $33.65   9.610%   $36.8838   $36.88   $36.90   $36.90  
  7 purchase totals = $724.83       $787.2998   $787.30   $787.25   $787.40