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 $61.55   11.259%   $68.4799   $68.48   $68.50   $68.50  
  Purchase #2 $80.66   11.828%   $90.2005   $90.20   $90.20   $90.20  
  Purchase #3 $199.74   6.592%   $212.9069   $212.91   $212.90   $212.90  
  Purchase #4 $39.97   4.143%   $41.626   $41.63   $41.65   $41.60  
  Purchase #5 $232.35   4.656%   $243.1682   $243.17   $243.15   $243.20  
  Purchase #6 $117.31   11.681%   $131.013   $131.01   $131.00   $131.00  
  Purchase #7 $136.91   6.849%   $146.287   $146.29   $146.30   $146.30  
  7 purchase totals = $868.49       $933.6815   $933.69   $933.70   $933.70