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 $43.40   12.521%   $48.8341   $48.83   $48.85   $48.80  
  Purchase #2 $235.67   9.450%   $257.9408   $257.94   $257.95   $257.90  
  Purchase #3 $53.95   11.326%   $60.0604   $60.06   $60.05   $60.10  
  Purchase #4 $211.32   6.700%   $225.4784   $225.48   $225.50   $225.50  
  Purchase #5 $235.75   12.123%   $264.33   $264.33   $264.35   $264.30  
  Purchase #6 $16.65   3.163%   $17.1766   $17.18   $17.20   $17.20  
  Purchase #7 $34.41   11.110%   $38.233   $38.23   $38.25   $38.20  
  7 purchase totals = $831.15       $912.0533   $912.05   $912.15   $912.00