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 $135.93   13.303%   $154.0128   $154.01   $154.00   $154.00  
  Purchase #2 $55.37   12.647%   $62.3726   $62.37   $62.35   $62.40  
  Purchase #3 $80.41   3.439%   $83.1753   $83.18   $83.20   $83.20  
  Purchase #4 $66.28   13.286%   $75.086   $75.09   $75.10   $75.10  
  Purchase #5 $178.92   12.291%   $200.9111   $200.91   $200.90   $200.90  
  Purchase #6 $73.82   12.605%   $83.125   $83.13   $83.15   $83.10  
  Purchase #7 $182.42   11.284%   $203.0043   $203.00   $203.00   $203.00  
  7 purchase totals = $773.15       $861.6871   $861.69   $861.70   $861.70