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 $198.96   5.818%   $210.5355   $210.54   $210.55   $210.50  
  Purchase #2 $134.49   12.162%   $150.8467   $150.85   $150.85   $150.80  
  Purchase #3 $155.84   5.698%   $164.7198   $164.72   $164.70   $164.70  
  Purchase #4 $204.38   9.567%   $223.933   $223.93   $223.95   $223.90  
  Purchase #5 $195.62   8.132%   $211.5278   $211.53   $211.55   $211.50  
  Purchase #6 $131.52   6.659%   $140.2779   $140.28   $140.30   $140.30  
  Purchase #7 $243.81   7.176%   $261.3058   $261.31   $261.30   $261.30  
  7 purchase totals = $1,264.62       $1,363.1465   $1,363.16   $1,363.20   $1,363.00