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 $228.36   6.476%   $243.1486   $243.15   $243.15   $243.10  
  Purchase #2 $126.78   11.596%   $141.4814   $141.48   $141.50   $141.50  
  Purchase #3 $43.43   3.121%   $44.7855   $44.79   $44.80   $44.80  
  Purchase #4 $244.40   11.804%   $273.249   $273.25   $273.25   $273.20  
  Purchase #5 $77.74   12.231%   $87.2484   $87.25   $87.25   $87.20  
  Purchase #6 $73.53   6.349%   $78.1984   $78.20   $78.20   $78.20  
  Purchase #7 $171.97   8.567%   $186.7027   $186.70   $186.70   $186.70  
  7 purchase totals = $966.21       $1,054.8140   $1,054.82   $1,054.85   $1,054.70