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 $76.97   13.796%   $87.5888   $87.59   $87.60   $87.60  
  Purchase #2 $157.26   4.349%   $164.0992   $164.10   $164.10   $164.10  
  Purchase #3 $118.68   3.801%   $123.191   $123.19   $123.20   $123.20  
  Purchase #4 $12.57   8.783%   $13.674   $13.67   $13.65   $13.70  
  Purchase #5 $241.60   3.336%   $249.6598   $249.66   $249.65   $249.70  
  Purchase #6 $208.83   11.495%   $232.835   $232.84   $232.85   $232.80  
  Purchase #7 $173.93   3.607%   $180.2037   $180.20   $180.20   $180.20  
  7 purchase totals = $989.84       $1,051.2515   $1,051.25   $1,051.25   $1,051.30