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 $25.87   3.235%   $26.7069   $26.71   $26.70   $26.70  
  Purchase #2 $95.57   7.476%   $102.7148   $102.71   $102.70   $102.70  
  Purchase #3 $237.35   3.820%   $246.4168   $246.42   $246.40   $246.40  
  Purchase #4 $144.34   4.409%   $150.704   $150.70   $150.70   $150.70  
  Purchase #5 $186.55   4.510%   $194.9634   $194.96   $194.95   $195.00  
  Purchase #6 $164.34   3.132%   $169.4871   $169.49   $169.50   $169.50  
  Purchase #7 $179.82   3.207%   $185.5868   $185.59   $185.60   $185.60  
  7 purchase totals = $1,033.84       $1,076.5798   $1,076.58   $1,076.55   $1,076.60