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 $23.33   11.197%   $25.9423   $25.94   $25.95   $25.90  
  Purchase #2 $219.72   6.322%   $233.6107   $233.61   $233.60   $233.60  
  Purchase #3 $88.46   7.807%   $95.3661   $95.37   $95.35   $95.40  
  Purchase #4 $174.77   5.600%   $184.5571   $184.56   $184.55   $184.60  
  Purchase #5 $168.97   6.124%   $179.3177   $179.32   $179.30   $179.30  
  Purchase #6 $212.39   8.715%   $230.8998   $230.90   $230.90   $230.90  
  Purchase #7 $43.76   8.692%   $47.5636   $47.56   $47.55   $47.60  
  7 purchase totals = $931.40       $997.2573   $997.26   $997.20   $997.30