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 $206.61   13.784%   $235.0891   $235.09   $235.10   $235.10  
  Purchase #2 $33.85   6.440%   $36.0299   $36.03   $36.05   $36.00  
  Purchase #3 $117.93   8.722%   $128.2159   $128.22   $128.20   $128.20  
  Purchase #4 $238.74   6.852%   $255.0985   $255.10   $255.10   $255.10  
  Purchase #5 $245.47   13.571%   $278.7827   $278.78   $278.80   $278.80  
  Purchase #6 $78.35   7.790%   $84.4535   $84.45   $84.45   $84.50  
  Purchase #7 $56.57   4.500%   $59.1157   $59.12   $59.10   $59.10  
  7 purchase totals = $977.52       $1,076.7853   $1,076.79   $1,076.80   $1,076.80