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 $49.97   7.758%   $53.8467   $53.85   $53.85   $53.80  
  Purchase #2 $154.97   4.319%   $161.6632   $161.66   $161.65   $161.70  
  Purchase #3 $98.98   8.628%   $107.52   $107.52   $107.50   $107.50  
  Purchase #4 $161.36   13.558%   $183.2372   $183.24   $183.25   $183.20  
  Purchase #5 $232.42   4.437%   $242.7325   $242.73   $242.75   $242.70  
  Purchase #6 $175.54   7.820%   $189.2672   $189.27   $189.25   $189.30  
  Purchase #7 $230.67   7.418%   $247.7811   $247.78   $247.80   $247.80  
  7 purchase totals = $1,103.91       $1,186.0479   $1,186.05   $1,186.05   $1,186.00