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 $55.33   8.567%   $60.0701   $60.07   $60.05   $60.10  
  Purchase #2 $245.79   8.368%   $266.3577   $266.36   $266.35   $266.40  
  Purchase #3 $167.94   9.577%   $184.0236   $184.02   $184.00   $184.00  
  Purchase #4 $19.89   13.214%   $22.5183   $22.52   $22.50   $22.50  
  Purchase #5 $158.96   11.776%   $177.6791   $177.68   $177.70   $177.70  
  Purchase #6 $227.43   13.180%   $257.4053   $257.41   $257.40   $257.40  
  Purchase #7 $51.40   3.614%   $53.2576   $53.26   $53.25   $53.30  
  7 purchase totals = $926.74       $1,021.3117   $1,021.32   $1,021.25   $1,021.40