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 $202.68   8.316%   $219.5349   $219.53   $219.55   $219.50  
  Purchase #2 $102.95   9.120%   $112.339   $112.34   $112.35   $112.30  
  Purchase #3 $151.65   9.806%   $166.5208   $166.52   $166.50   $166.50  
  Purchase #4 $245.76   8.612%   $266.9249   $266.92   $266.90   $266.90  
  Purchase #5 $107.66   6.696%   $114.8689   $114.87   $114.85   $114.90  
  Purchase #6 $39.68   10.705%   $43.9277   $43.93   $43.95   $43.90  
  Purchase #7 $234.91   5.123%   $246.9444   $246.94   $246.95   $246.90  
  7 purchase totals = $1,085.29       $1,171.0606   $1,171.05   $1,171.05   $1,170.90