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 $61.93   12.492%   $69.6663   $69.67   $69.65   $69.70  
  Purchase #2 $178.89   7.559%   $192.4123   $192.41   $192.40   $192.40  
  Purchase #3 $224.85   10.142%   $247.6543   $247.65   $247.65   $247.70  
  Purchase #4 $112.75   12.481%   $126.8223   $126.82   $126.80   $126.80  
  Purchase #5 $186.69   8.251%   $202.0938   $202.09   $202.10   $202.10  
  Purchase #6 $166.39   8.690%   $180.8493   $180.85   $180.85   $180.80  
  Purchase #7 $41.64   13.515%   $47.2676   $47.27   $47.25   $47.30  
  7 purchase totals = $973.14       $1,066.7659   $1,066.76   $1,066.70   $1,066.80