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 $66.53   12.152%   $74.6147   $74.61   $74.60   $74.60  
  Purchase #2 $191.53   3.831%   $198.8675   $198.87   $198.85   $198.90  
  Purchase #3 $239.82   10.155%   $264.1737   $264.17   $264.15   $264.20  
  Purchase #4 $200.72   5.716%   $212.1932   $212.19   $212.20   $212.20  
  Purchase #5 $135.56   3.816%   $140.733   $140.73   $140.75   $140.70  
  Purchase #6 $197.71   6.864%   $211.2808   $211.28   $211.30   $211.30  
  Purchase #7 $215.33   6.825%   $230.0263   $230.03   $230.05   $230.00  
  7 purchase totals = $1,247.20       $1,331.8892   $1,331.88   $1,331.90   $1,331.90