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 $51.29   10.411%   $56.6298   $56.63   $56.65   $56.60  
  Purchase #2 $31.80   8.873%   $34.6216   $34.62   $34.60   $34.60  
  Purchase #3 $75.58   6.480%   $80.4776   $80.48   $80.50   $80.50  
  Purchase #4 $43.49   3.857%   $45.1674   $45.17   $45.15   $45.20  
  Purchase #5 $177.50   3.603%   $183.8953   $183.90   $183.90   $183.90  
  Purchase #6 $175.63   9.444%   $192.2165   $192.22   $192.20   $192.20  
  Purchase #7 $166.44   4.543%   $174.0014   $174.00   $174.00   $174.00  
  7 purchase totals = $721.73       $767.0096   $767.02   $767.00   $767.00