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   3.144%   $63.8771   $63.88   $63.90   $63.90  
  Purchase #2 $99.34   11.281%   $110.5465   $110.55   $110.55   $110.50  
  Purchase #3 $231.48   5.295%   $243.7369   $243.74   $243.75   $243.70  
  Purchase #4 $143.65   6.827%   $153.457   $153.46   $153.45   $153.50  
  Purchase #5 $48.39   7.314%   $51.9292   $51.93   $51.95   $51.90  
  Purchase #6 $163.79   8.811%   $178.2215   $178.22   $178.20   $178.20  
  Purchase #7 $183.45   12.488%   $206.3592   $206.36   $206.35   $206.40  
  7 purchase totals = $932.03       $1,008.1274   $1,008.14   $1,008.15   $1,008.10