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 $238.39   3.543%   $246.8362   $246.84   $246.85   $246.80  
  Purchase #2 $203.69   13.734%   $231.6648   $231.66   $231.65   $231.70  
  Purchase #3 $41.48   7.491%   $44.5873   $44.59   $44.60   $44.60  
  Purchase #4 $84.31   9.267%   $92.123   $92.12   $92.10   $92.10  
  Purchase #5 $231.86   13.239%   $262.5559   $262.56   $262.55   $262.60  
  Purchase #6 $10.96   13.628%   $12.4536   $12.45   $12.45   $12.50  
  Purchase #7 $239.66   6.478%   $255.1852   $255.19   $255.20   $255.20  
  7 purchase totals = $1,050.35       $1,145.4060   $1,145.41   $1,145.40   $1,145.50