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 $200.50   5.248%   $211.0222   $211.02   $211.00   $211.00  
  Purchase #2 $134.90   11.573%   $150.512   $150.51   $150.50   $150.50  
  Purchase #3 $65.84   5.806%   $69.6627   $69.66   $69.65   $69.70  
  Purchase #4 $94.93   12.264%   $106.5722   $106.57   $106.55   $106.60  
  Purchase #5 $192.37   13.648%   $218.6247   $218.62   $218.60   $218.60  
  Purchase #6 $48.36   7.226%   $51.8545   $51.85   $51.85   $51.90  
  Purchase #7 $71.36   10.246%   $78.6715   $78.67   $78.65   $78.70  
  7 purchase totals = $808.26       $886.9198   $886.90   $886.80   $887.00