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 $205.68   12.852%   $232.114   $232.11   $232.10   $232.10  
  Purchase #2 $201.60   8.118%   $217.9659   $217.97   $217.95   $218.00  
  Purchase #3 $250.76   8.692%   $272.5561   $272.56   $272.55   $272.60  
  Purchase #4 $224.58   9.470%   $245.8477   $245.85   $245.85   $245.80  
  Purchase #5 $196.84   13.305%   $223.0296   $223.03   $223.05   $223.00  
  Purchase #6 $236.63   6.186%   $251.2679   $251.27   $251.25   $251.30  
  Purchase #7 $250.47   3.216%   $258.5251   $258.53   $258.55   $258.50  
  7 purchase totals = $1,566.56       $1,701.3063   $1,701.32   $1,701.30   $1,701.30