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 $78.59   11.861%   $87.9116   $87.91   $87.90   $87.90  
  Purchase #2 $119.82   6.471%   $127.5736   $127.57   $127.55   $127.60  
  Purchase #3 $204.41   3.326%   $211.2087   $211.21   $211.20   $211.20  
  Purchase #4 $221.84   12.461%   $249.4835   $249.48   $249.50   $249.50  
  Purchase #5 $127.94   6.610%   $136.3968   $136.40   $136.40   $136.40  
  Purchase #6 $197.44   4.790%   $206.8974   $206.90   $206.90   $206.90  
  Purchase #7 $24.58   5.373%   $25.9007   $25.90   $25.90   $25.90  
  7 purchase totals = $974.62       $1,045.3723   $1,045.37   $1,045.35   $1,045.40