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 $166.97   10.366%   $184.2781   $184.28   $184.30   $184.30  
  Purchase #2 $223.92   6.284%   $237.9911   $237.99   $238.00   $238.00  
  Purchase #3 $189.72   6.310%   $201.6913   $201.69   $201.70   $201.70  
  Purchase #4 $94.46   13.865%   $107.5569   $107.56   $107.55   $107.60  
  Purchase #5 $27.77   9.187%   $30.3212   $30.32   $30.30   $30.30  
  Purchase #6 $118.44   6.339%   $125.9479   $125.95   $125.95   $125.90  
  Purchase #7 $125.85   8.593%   $136.6643   $136.66   $136.65   $136.70  
  7 purchase totals = $947.13       $1,024.4508   $1,024.45   $1,024.45   $1,024.50