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 $44.79   8.648%   $48.6634   $48.66   $48.65   $48.70  
  Purchase #2 $132.60   9.869%   $145.6863   $145.69   $145.70   $145.70  
  Purchase #3 $249.56   11.354%   $277.895   $277.90   $277.90   $277.90  
  Purchase #4 $140.56   6.509%   $149.7091   $149.71   $149.70   $149.70  
  Purchase #5 $57.58   5.664%   $60.8413   $60.84   $60.85   $60.80  
  Purchase #6 $104.80   13.380%   $118.8222   $118.82   $118.80   $118.80  
  Purchase #7 $196.32   12.414%   $220.6912   $220.69   $220.70   $220.70  
  7 purchase totals = $926.21       $1,022.3085   $1,022.31   $1,022.30   $1,022.30