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 $236.58   5.517%   $249.6321   $249.63   $249.65   $249.60  
  Purchase #2 $31.93   7.650%   $34.3726   $34.37   $34.35   $34.40  
  Purchase #3 $202.52   5.113%   $212.8748   $212.87   $212.85   $212.90  
  Purchase #4 $147.70   6.159%   $156.7968   $156.80   $156.80   $156.80  
  Purchase #5 $225.31   12.135%   $252.6514   $252.65   $252.65   $252.70  
  Purchase #6 $18.84   12.149%   $21.1289   $21.13   $21.15   $21.10  
  Purchase #7 $92.47   6.615%   $98.5869   $98.59   $98.60   $98.60  
  7 purchase totals = $955.35       $1,026.0435   $1,026.04   $1,026.05   $1,026.10