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 $155.70   12.790%   $175.614   $175.61   $175.60   $175.60  
  Purchase #2 $31.67   6.103%   $33.6028   $33.60   $33.60   $33.60  
  Purchase #3 $206.42   3.158%   $212.9387   $212.94   $212.95   $212.90  
  Purchase #4 $232.83   5.503%   $245.6426   $245.64   $245.65   $245.60  
  Purchase #5 $77.35   4.870%   $81.1169   $81.12   $81.10   $81.10  
  Purchase #6 $147.64   9.220%   $161.2524   $161.25   $161.25   $161.30  
  Purchase #7 $135.95   13.438%   $154.219   $154.22   $154.20   $154.20  
  7 purchase totals = $987.56       $1,064.3864   $1,064.38   $1,064.35   $1,064.30