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 $57.64   10.770%   $63.8478   $63.85   $63.85   $63.80  
  Purchase #2 $165.79   11.119%   $184.2242   $184.22   $184.20   $184.20  
  Purchase #3 $115.36   6.148%   $122.4523   $122.45   $122.45   $122.50  
  Purchase #4 $83.39   12.451%   $93.7729   $93.77   $93.75   $93.80  
  Purchase #5 $174.76   5.460%   $184.3019   $184.30   $184.30   $184.30  
  Purchase #6 $213.41   9.184%   $233.0096   $233.01   $233.00   $233.00  
  Purchase #7 $240.92   7.107%   $258.0422   $258.04   $258.05   $258.00  
  7 purchase totals = $1,051.27       $1,139.6509   $1,139.64   $1,139.60   $1,139.60