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 $62.78   5.349%   $66.1381   $66.14   $66.15   $66.10  
  Purchase #2 $21.48   13.805%   $24.4453   $24.45   $24.45   $24.40  
  Purchase #3 $99.55   13.611%   $113.0998   $113.10   $113.10   $113.10  
  Purchase #4 $53.50   4.112%   $55.6999   $55.70   $55.70   $55.70  
  Purchase #5 $226.26   6.607%   $241.209   $241.21   $241.20   $241.20  
  Purchase #6 $82.42   8.125%   $89.1166   $89.12   $89.10   $89.10  
  Purchase #7 $155.98   8.472%   $169.1946   $169.19   $169.20   $169.20  
  7 purchase totals = $701.97       $758.9033   $758.91   $758.90   $758.80