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 $207.57   11.690%   $231.8349   $231.83   $231.85   $231.80  
  Purchase #2 $240.99   13.511%   $273.5502   $273.55   $273.55   $273.60  
  Purchase #3 $25.71   8.427%   $27.8766   $27.88   $27.90   $27.90  
  Purchase #4 $173.47   12.102%   $194.4633   $194.46   $194.45   $194.50  
  Purchase #5 $217.33   3.293%   $224.4867   $224.49   $224.50   $224.50  
  Purchase #6 $65.73   11.557%   $73.3264   $73.33   $73.35   $73.30  
  Purchase #7 $116.88   8.622%   $126.9574   $126.96   $126.95   $127.00  
  7 purchase totals = $1,047.68       $1,152.4955   $1,152.50   $1,152.55   $1,152.60