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 $100.29   3.168%   $103.4672   $103.47   $103.45   $103.50  
  Purchase #2 $171.53   3.809%   $178.0636   $178.06   $178.05   $178.10  
  Purchase #3 $75.60   10.431%   $83.4858   $83.49   $83.50   $83.50  
  Purchase #4 $226.94   8.200%   $245.5491   $245.55   $245.55   $245.50  
  Purchase #5 $88.32   3.533%   $91.4403   $91.44   $91.45   $91.40  
  Purchase #6 $13.55   12.392%   $15.2291   $15.23   $15.25   $15.20  
  Purchase #7 $124.74   4.205%   $129.9853   $129.99   $130.00   $130.00  
  7 purchase totals = $800.97       $847.2204   $847.23   $847.25   $847.20