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 $41.34   11.354%   $46.0337   $46.03   $46.05   $46.00  
  Purchase #2 $197.45   7.783%   $212.8175   $212.82   $212.80   $212.80  
  Purchase #3 $171.94   12.562%   $193.5391   $193.54   $193.55   $193.50  
  Purchase #4 $58.30   5.472%   $61.4902   $61.49   $61.50   $61.50  
  Purchase #5 $95.87   3.377%   $99.1075   $99.11   $99.10   $99.10  
  Purchase #6 $100.48   13.132%   $113.675   $113.68   $113.70   $113.70  
  Purchase #7 $174.29   6.352%   $185.3609   $185.36   $185.35   $185.40  
  7 purchase totals = $839.67       $912.0239   $912.03   $912.05   $912.00