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 $206.57   13.395%   $234.2401   $234.24   $234.25   $234.20  
  Purchase #2 $48.95   13.754%   $55.6826   $55.68   $55.70   $55.70  
  Purchase #3 $72.94   3.735%   $75.6643   $75.66   $75.65   $75.70  
  Purchase #4 $195.60   4.372%   $204.1516   $204.15   $204.15   $204.20  
  Purchase #5 $181.50   10.599%   $200.7372   $200.74   $200.75   $200.70  
  Purchase #6 $34.92   7.212%   $37.4384   $37.44   $37.45   $37.40  
  Purchase #7 $237.51   3.752%   $246.4214   $246.42   $246.40   $246.40  
  7 purchase totals = $977.99       $1,054.3356   $1,054.33   $1,054.35   $1,054.30