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 $51.68   13.567%   $58.6914   $58.69   $58.70   $58.70  
  Purchase #2 $230.54   12.702%   $259.8232   $259.82   $259.80   $259.80  
  Purchase #3 $169.41   11.515%   $188.9176   $188.92   $188.90   $188.90  
  Purchase #4 $142.87   4.697%   $149.5806   $149.58   $149.60   $149.60  
  Purchase #5 $156.62   6.801%   $167.2717   $167.27   $167.25   $167.30  
  Purchase #6 $25.73   6.347%   $27.3631   $27.36   $27.35   $27.40  
  Purchase #7 $201.83   5.296%   $212.5189   $212.52   $212.50   $212.50  
  7 purchase totals = $978.68       $1,064.1665   $1,064.16   $1,064.10   $1,064.20