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 $86.60   13.407%   $98.2105   $98.21   $98.20   $98.20  
  Purchase #2 $159.75   9.370%   $174.7186   $174.72   $174.70   $174.70  
  Purchase #3 $90.39   6.397%   $96.1722   $96.17   $96.15   $96.20  
  Purchase #4 $232.42   13.535%   $263.878   $263.88   $263.90   $263.90  
  Purchase #5 $194.47   9.550%   $213.0419   $213.04   $213.05   $213.00  
  Purchase #6 $5.78   12.145%   $6.482   $6.48   $6.50   $6.50  
  Purchase #7 $198.98   13.118%   $225.0822   $225.08   $225.10   $225.10  
  7 purchase totals = $968.39       $1,077.5854   $1,077.58   $1,077.60   $1,077.60