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 $118.83   6.108%   $126.0881   $126.09   $126.10   $126.10  
  Purchase #2 $91.89   12.340%   $103.2292   $103.23   $103.25   $103.20  
  Purchase #3 $19.72   12.244%   $22.1345   $22.13   $22.15   $22.10  
  Purchase #4 $61.52   6.839%   $65.7274   $65.73   $65.75   $65.70  
  Purchase #5 $165.50   7.122%   $177.2869   $177.29   $177.30   $177.30  
  Purchase #6 $47.72   13.665%   $54.2409   $54.24   $54.25   $54.20  
  Purchase #7 $8.71   5.659%   $9.2029   $9.20   $9.20   $9.20  
  7 purchase totals = $513.89       $557.9099   $557.91   $558.00   $557.80