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 $246.88   6.738%   $263.5148   $263.51   $263.50   $263.50  
  Purchase #2 $74.98   3.597%   $77.677   $77.68   $77.70   $77.70  
  Purchase #3 $57.34   4.383%   $59.8532   $59.85   $59.85   $59.90  
  Purchase #4 $184.94   6.728%   $197.3828   $197.38   $197.40   $197.40  
  Purchase #5 $194.51   12.166%   $218.1741   $218.17   $218.15   $218.20  
  Purchase #6 $66.55   12.682%   $74.9899   $74.99   $75.00   $75.00  
  Purchase #7 $199.72   3.139%   $205.9892   $205.99   $206.00   $206.00  
  7 purchase totals = $1,024.92       $1,097.5810   $1,097.57   $1,097.60   $1,097.70