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 $122.55   3.198%   $126.4691   $126.47   $126.45   $126.50  
  Purchase #2 $89.74   5.134%   $94.3473   $94.35   $94.35   $94.30  
  Purchase #3 $61.79   11.187%   $68.7024   $68.70   $68.70   $68.70  
  Purchase #4 $164.42   5.824%   $173.9958   $174.00   $174.00   $174.00  
  Purchase #5 $50.41   13.553%   $57.2421   $57.24   $57.25   $57.20  
  Purchase #6 $54.56   13.268%   $61.799   $61.80   $61.80   $61.80  
  Purchase #7 $145.90   4.140%   $151.9403   $151.94   $151.95   $151.90  
  7 purchase totals = $689.37       $734.4960   $734.50   $734.50   $734.40