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 $211.94   10.265%   $233.6956   $233.70   $233.70   $233.70  
  Purchase #2 $64.92   5.780%   $68.6724   $68.67   $68.65   $68.70  
  Purchase #3 $123.95   8.667%   $134.6927   $134.69   $134.70   $134.70  
  Purchase #4 $156.97   7.294%   $168.4194   $168.42   $168.40   $168.40  
  Purchase #5 $59.52   6.756%   $63.5412   $63.54   $63.55   $63.50  
  Purchase #6 $55.47   6.186%   $58.9014   $58.90   $58.90   $58.90  
  Purchase #7 $166.25   9.809%   $182.5575   $182.56   $182.55   $182.60  
  7 purchase totals = $839.02       $910.4802   $910.48   $910.45   $910.50