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 $223.29   10.602%   $246.9632   $246.96   $246.95   $247.00  
  Purchase #2 $206.80   11.563%   $230.7123   $230.71   $230.70   $230.70  
  Purchase #3 $113.34   4.427%   $118.3576   $118.36   $118.35   $118.40  
  Purchase #4 $214.59   12.863%   $242.1927   $242.19   $242.20   $242.20  
  Purchase #5 $45.77   6.171%   $48.5945   $48.59   $48.60   $48.60  
  Purchase #6 $121.91   9.160%   $133.077   $133.08   $133.10   $133.10  
  Purchase #7 $68.62   11.231%   $76.3267   $76.33   $76.35   $76.30  
  7 purchase totals = $994.32       $1,096.2240   $1,096.22   $1,096.25   $1,096.30