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 $214.27   10.717%   $237.2333   $237.23   $237.25   $237.20  
  Purchase #2 $10.57   11.732%   $11.8101   $11.81   $11.80   $11.80  
  Purchase #3 $8.85   9.607%   $9.7002   $9.70   $9.70   $9.70  
  Purchase #4 $41.88   13.587%   $47.5702   $47.57   $47.55   $47.60  
  Purchase #5 $173.90   3.435%   $179.8735   $179.87   $179.85   $179.90  
  Purchase #6 $22.56   4.615%   $23.6011   $23.60   $23.60   $23.60  
  Purchase #7 $238.26   3.413%   $246.3918   $246.39   $246.40   $246.40  
  7 purchase totals = $710.29       $756.1802   $756.17   $756.15   $756.20