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 $209.41   12.503%   $235.5925   $235.59   $235.60   $235.60  
  Purchase #2 $88.81   6.585%   $94.6581   $94.66   $94.65   $94.70  
  Purchase #3 $170.36   9.637%   $186.7776   $186.78   $186.80   $186.80  
  Purchase #4 $32.94   6.476%   $35.0732   $35.07   $35.05   $35.10  
  Purchase #5 $66.79   5.600%   $70.5302   $70.53   $70.55   $70.50  
  Purchase #6 $245.49   7.447%   $263.7716   $263.77   $263.75   $263.80  
  Purchase #7 $231.44   7.504%   $248.8073   $248.81   $248.80   $248.80  
  7 purchase totals = $1,045.24       $1,135.2105   $1,135.21   $1,135.20   $1,135.30