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 $185.40   6.558%   $197.5585   $197.56   $197.55   $197.60  
  Purchase #2 $241.90   4.870%   $253.6805   $253.68   $253.70   $253.70  
  Purchase #3 $95.64   12.530%   $107.6237   $107.62   $107.60   $107.60  
  Purchase #4 $117.28   9.530%   $128.4568   $128.46   $128.45   $128.50  
  Purchase #5 $99.85   12.656%   $112.487   $112.49   $112.50   $112.50  
  Purchase #6 $24.30   12.342%   $27.2991   $27.30   $27.30   $27.30  
  Purchase #7 $177.60   9.828%   $195.0545   $195.05   $195.05   $195.10  
  7 purchase totals = $941.97       $1,022.1601   $1,022.16   $1,022.15   $1,022.30