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 $40.68   12.257%   $45.6661   $45.67   $45.65   $45.70  
  Purchase #2 $56.47   11.703%   $63.0787   $63.08   $63.10   $63.10  
  Purchase #3 $238.85   11.797%   $267.0271   $267.03   $267.05   $267.00  
  Purchase #4 $248.37   4.375%   $259.2362   $259.24   $259.25   $259.20  
  Purchase #5 $65.62   12.644%   $73.917   $73.92   $73.90   $73.90  
  Purchase #6 $58.41   5.582%   $61.6704   $61.67   $61.65   $61.70  
  Purchase #7 $179.48   8.532%   $194.7932   $194.79   $194.80   $194.80  
  7 purchase totals = $887.88       $965.3887   $965.40   $965.40   $965.40