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 $248.64   3.832%   $258.1679   $258.17   $258.15   $258.20  
  Purchase #2 $157.92   6.789%   $168.6412   $168.64   $168.65   $168.60  
  Purchase #3 $69.71   11.279%   $77.5726   $77.57   $77.55   $77.60  
  Purchase #4 $227.68   6.820%   $243.2078   $243.21   $243.20   $243.20  
  Purchase #5 $113.71   11.266%   $126.5206   $126.52   $126.50   $126.50  
  Purchase #6 $168.94   4.133%   $175.9223   $175.92   $175.90   $175.90  
  Purchase #7 $109.37   7.437%   $117.5038   $117.50   $117.50   $117.50  
  7 purchase totals = $1,095.97       $1,167.5362   $1,167.53   $1,167.45   $1,167.50