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 $192.63   6.400%   $204.9583   $204.96   $204.95   $205.00  
  Purchase #2 $131.99   8.422%   $143.1062   $143.11   $143.10   $143.10  
  Purchase #3 $45.57   13.213%   $51.5912   $51.59   $51.60   $51.60  
  Purchase #4 $57.83   9.798%   $63.4962   $63.50   $63.50   $63.50  
  Purchase #5 $236.69   13.108%   $267.7153   $267.72   $267.70   $267.70  
  Purchase #6 $65.46   3.372%   $67.6673   $67.67   $67.65   $67.70  
  Purchase #7 $119.49   3.495%   $123.6662   $123.67   $123.65   $123.70  
  7 purchase totals = $849.66       $922.2007   $922.22   $922.15   $922.30