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 $19.96   10.342%   $22.0243   $22.02   $22.00   $22.00  
  Purchase #2 $206.62   9.769%   $226.8047   $226.80   $226.80   $226.80  
  Purchase #3 $162.59   3.722%   $168.6416   $168.64   $168.65   $168.60  
  Purchase #4 $247.32   8.603%   $268.5969   $268.60   $268.60   $268.60  
  Purchase #5 $138.93   9.388%   $151.9727   $151.97   $151.95   $152.00  
  Purchase #6 $139.45   5.727%   $147.4363   $147.44   $147.45   $147.40  
  Purchase #7 $26.44   12.757%   $29.813   $29.81   $29.80   $29.80  
  7 purchase totals = $941.31       $1,015.2895   $1,015.28   $1,015.25   $1,015.20