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 $246.81   11.209%   $274.4749   $274.47   $274.45   $274.50  
  Purchase #2 $20.27   7.607%   $21.8119   $21.81   $21.80   $21.80  
  Purchase #3 $201.51   8.692%   $219.0252   $219.03   $219.05   $219.00  
  Purchase #4 $159.49   10.279%   $175.884   $175.88   $175.90   $175.90  
  Purchase #5 $225.79   8.707%   $245.4495   $245.45   $245.45   $245.40  
  Purchase #6 $89.43   6.231%   $95.0024   $95.00   $95.00   $95.00  
  Purchase #7 $80.46   7.434%   $86.4414   $86.44   $86.45   $86.40  
  7 purchase totals = $1,023.76       $1,118.0893   $1,118.08   $1,118.10   $1,118.00