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 $69.44   10.284%   $76.5812   $76.58   $76.60   $76.60  
  Purchase #2 $158.41   7.822%   $170.8008   $170.80   $170.80   $170.80  
  Purchase #3 $144.99   4.598%   $151.6566   $151.66   $151.65   $151.70  
  Purchase #4 $185.25   10.500%   $204.7013   $204.70   $204.70   $204.70  
  Purchase #5 $62.76   11.130%   $69.7452   $69.75   $69.75   $69.70  
  Purchase #6 $9.31   9.779%   $10.2204   $10.22   $10.20   $10.20  
  Purchase #7 $19.68   11.816%   $22.0054   $22.01   $22.00   $22.00  
  7 purchase totals = $649.84       $705.7109   $705.72   $705.70   $705.70