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 $196.25   5.661%   $207.3597   $207.36   $207.35   $207.40  
  Purchase #2 $54.92   6.265%   $58.3607   $58.36   $58.35   $58.40  
  Purchase #3 $77.86   12.440%   $87.5458   $87.55   $87.55   $87.50  
  Purchase #4 $64.56   11.212%   $71.7985   $71.80   $71.80   $71.80  
  Purchase #5 $159.40   6.324%   $169.4805   $169.48   $169.50   $169.50  
  Purchase #6 $221.96   8.158%   $240.0675   $240.07   $240.05   $240.10  
  Purchase #7 $36.63   6.505%   $39.0128   $39.01   $39.00   $39.00  
  7 purchase totals = $811.58       $873.6255   $873.63   $873.60   $873.70