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 $184.97   11.147%   $205.5886   $205.59   $205.60   $205.60  
  Purchase #2 $83.75   9.528%   $91.7297   $91.73   $91.75   $91.70  
  Purchase #3 $42.55   9.140%   $46.4391   $46.44   $46.45   $46.40  
  Purchase #4 $108.48   8.715%   $117.934   $117.93   $117.95   $117.90  
  Purchase #5 $207.91   11.310%   $231.4246   $231.42   $231.40   $231.40  
  Purchase #6 $144.64   4.178%   $150.6831   $150.68   $150.70   $150.70  
  Purchase #7 $171.93   3.585%   $178.0937   $178.09   $178.10   $178.10  
  7 purchase totals = $944.23       $1,021.8928   $1,021.88   $1,021.95   $1,021.80