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 $63.94   5.810%   $67.6549   $67.65   $67.65   $67.70  
  Purchase #2 $11.34   12.210%   $12.7246   $12.72   $12.70   $12.70  
  Purchase #3 $147.91   11.330%   $164.6682   $164.67   $164.65   $164.70  
  Purchase #4 $17.96   9.379%   $19.6445   $19.64   $19.65   $19.60  
  Purchase #5 $225.94   3.831%   $234.5958   $234.60   $234.60   $234.60  
  Purchase #6 $247.25   12.248%   $277.5332   $277.53   $277.55   $277.50  
  Purchase #7 $150.66   12.715%   $169.8164   $169.82   $169.80   $169.80  
  7 purchase totals = $865.00       $946.6376   $946.63   $946.60   $946.60