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 $176.60   9.113%   $192.6936   $192.69   $192.70   $192.70  
  Purchase #2 $76.68   7.302%   $82.2792   $82.28   $82.30   $82.30  
  Purchase #3 $102.95   8.700%   $111.9067   $111.91   $111.90   $111.90  
  Purchase #4 $24.81   6.793%   $26.4953   $26.50   $26.50   $26.50  
  Purchase #5 $235.82   6.698%   $251.6152   $251.62   $251.60   $251.60  
  Purchase #6 $112.72   7.576%   $121.2597   $121.26   $121.25   $121.30  
  Purchase #7 $238.37   13.482%   $270.507   $270.51   $270.50   $270.50  
  7 purchase totals = $967.95       $1,056.7567   $1,056.77   $1,056.75   $1,056.80