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 $76.46   9.647%   $83.8361   $83.84   $83.85   $83.80  
  Purchase #2 $202.40   8.347%   $219.2943   $219.29   $219.30   $219.30  
  Purchase #3 $166.42   13.262%   $188.4906   $188.49   $188.50   $188.50  
  Purchase #4 $85.91   12.640%   $96.769   $96.77   $96.75   $96.80  
  Purchase #5 $215.75   11.469%   $240.4944   $240.49   $240.50   $240.50  
  Purchase #6 $246.40   4.715%   $258.0178   $258.02   $258.00   $258.00  
  Purchase #7 $246.54   9.605%   $270.2202   $270.22   $270.20   $270.20  
  7 purchase totals = $1,239.88       $1,357.1224   $1,357.12   $1,357.10   $1,357.10