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 $14.89   11.437%   $16.593   $16.59   $16.60   $16.60  
  Purchase #2 $202.25   12.160%   $226.8436   $226.84   $226.85   $226.80  
  Purchase #3 $6.46   7.457%   $6.9417   $6.94   $6.95   $6.90  
  Purchase #4 $177.47   7.774%   $191.2665   $191.27   $191.25   $191.30  
  Purchase #5 $234.48   13.477%   $266.0809   $266.08   $266.10   $266.10  
  Purchase #6 $188.97   11.158%   $210.0553   $210.06   $210.05   $210.10  
  Purchase #7 $148.56   13.381%   $168.4388   $168.44   $168.45   $168.40  
  7 purchase totals = $973.08       $1,086.2198   $1,086.22   $1,086.25   $1,086.20