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 $180.88   11.463%   $201.6143   $201.61   $201.60   $201.60  
  Purchase #2 $79.83   5.851%   $84.5009   $84.50   $84.50   $84.50  
  Purchase #3 $91.31   9.184%   $99.6959   $99.70   $99.70   $99.70  
  Purchase #4 $63.37   4.213%   $66.0398   $66.04   $66.05   $66.00  
  Purchase #5 $181.34   10.861%   $201.0353   $201.04   $201.05   $201.00  
  Purchase #6 $53.56   4.288%   $55.8567   $55.86   $55.85   $55.90  
  Purchase #7 $69.97   5.292%   $73.6728   $73.67   $73.65   $73.70  
  7 purchase totals = $720.26       $782.4157   $782.42   $782.40   $782.40