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 $207.75   7.776%   $223.9046   $223.90   $223.90   $223.90  
  Purchase #2 $60.43   8.414%   $65.5146   $65.51   $65.50   $65.50  
  Purchase #3 $179.98   7.277%   $193.0771   $193.08   $193.10   $193.10  
  Purchase #4 $66.58   5.164%   $70.0182   $70.02   $70.00   $70.00  
  Purchase #5 $10.95   6.206%   $11.6296   $11.63   $11.65   $11.60  
  Purchase #6 $239.57   4.773%   $251.0047   $251.00   $251.00   $251.00  
  Purchase #7 $241.54   9.283%   $263.9622   $263.96   $263.95   $264.00  
  7 purchase totals = $1,006.80       $1,079.1110   $1,079.10   $1,079.10   $1,079.10