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 $188.72   5.606%   $199.2996   $199.30   $199.30   $199.30  
  Purchase #2 $220.57   7.554%   $237.2319   $237.23   $237.25   $237.20  
  Purchase #3 $204.81   12.581%   $230.5771   $230.58   $230.60   $230.60  
  Purchase #4 $99.94   5.591%   $105.5276   $105.53   $105.55   $105.50  
  Purchase #5 $245.48   9.108%   $267.8383   $267.84   $267.85   $267.80  
  Purchase #6 $26.25   11.652%   $29.3087   $29.31   $29.30   $29.30  
  Purchase #7 $22.66   4.609%   $23.7044   $23.70   $23.70   $23.70  
  7 purchase totals = $1,008.43       $1,093.4876   $1,093.49   $1,093.55   $1,093.40