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 $194.87   8.378%   $211.1962   $211.20   $211.20   $211.20  
  Purchase #2 $71.32   7.167%   $76.4315   $76.43   $76.45   $76.40  
  Purchase #3 $44.66   3.689%   $46.3075   $46.31   $46.30   $46.30  
  Purchase #4 $48.37   7.424%   $51.961   $51.96   $51.95   $52.00  
  Purchase #5 $83.53   5.479%   $88.1066   $88.11   $88.10   $88.10  
  Purchase #6 $173.72   7.861%   $187.3761   $187.38   $187.40   $187.40  
  Purchase #7 $100.66   8.833%   $109.5513   $109.55   $109.55   $109.60  
  7 purchase totals = $717.13       $770.9302   $770.94   $770.95   $771.00