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 $20.78   4.151%   $21.6426   $21.64   $21.65   $21.60  
  Purchase #2 $62.69   5.211%   $65.9568   $65.96   $65.95   $66.00  
  Purchase #3 $139.68   8.356%   $151.3517   $151.35   $151.35   $151.40  
  Purchase #4 $231.70   8.641%   $251.7212   $251.72   $251.70   $251.70  
  Purchase #5 $161.42   12.264%   $181.2165   $181.22   $181.20   $181.20  
  Purchase #6 $179.54   9.364%   $196.3521   $196.35   $196.35   $196.40  
  Purchase #7 $235.31   10.647%   $260.3635   $260.36   $260.35   $260.40  
  7 purchase totals = $1,031.12       $1,128.6044   $1,128.60   $1,128.55   $1,128.70