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 $232.57   13.190%   $263.246   $263.25   $263.25   $263.20  
  Purchase #2 $173.57   8.566%   $188.438   $188.44   $188.45   $188.40  
  Purchase #3 $21.50   9.471%   $23.5363   $23.54   $23.55   $23.50  
  Purchase #4 $63.37   12.723%   $71.4326   $71.43   $71.45   $71.40  
  Purchase #5 $50.44   6.612%   $53.7751   $53.78   $53.80   $53.80  
  Purchase #6 $230.99   12.785%   $260.5221   $260.52   $260.50   $260.50  
  Purchase #7 $223.83   10.755%   $247.9029   $247.90   $247.90   $247.90  
  7 purchase totals = $996.27       $1,108.8530   $1,108.86   $1,108.90   $1,108.70