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 $157.27   12.657%   $177.1757   $177.18   $177.20   $177.20  
  Purchase #2 $110.29   11.455%   $122.9237   $122.92   $122.90   $122.90  
  Purchase #3 $161.94   8.550%   $175.7859   $175.79   $175.80   $175.80  
  Purchase #4 $246.25   7.114%   $263.7682   $263.77   $263.75   $263.80  
  Purchase #5 $232.64   5.600%   $245.6678   $245.67   $245.65   $245.70  
  Purchase #6 $229.69   13.142%   $259.8759   $259.88   $259.90   $259.90  
  Purchase #7 $55.60   11.219%   $61.8378   $61.84   $61.85   $61.80  
  7 purchase totals = $1,193.68       $1,307.0350   $1,307.05   $1,307.05   $1,307.10