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 $214.86   12.173%   $241.0149   $241.01   $241.00   $241.00  
  Purchase #2 $146.87   9.437%   $160.7301   $160.73   $160.75   $160.70  
  Purchase #3 $121.62   9.241%   $132.8589   $132.86   $132.85   $132.90  
  Purchase #4 $45.43   13.294%   $51.4695   $51.47   $51.45   $51.50  
  Purchase #5 $161.76   12.273%   $181.6128   $181.61   $181.60   $181.60  
  Purchase #6 $154.69   6.336%   $164.4912   $164.49   $164.50   $164.50  
  Purchase #7 $116.70   9.656%   $127.9686   $127.97   $127.95   $128.00  
  7 purchase totals = $961.93       $1,060.1460   $1,060.14   $1,060.10   $1,060.20