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 $62.83   8.237%   $68.0053   $68.01   $68.00   $68.00  
  Purchase #2 $33.55   10.297%   $37.0046   $37.00   $37.00   $37.00  
  Purchase #3 $247.28   12.104%   $277.2108   $277.21   $277.20   $277.20  
  Purchase #4 $62.37   12.791%   $70.3477   $70.35   $70.35   $70.30  
  Purchase #5 $159.86   13.694%   $181.7512   $181.75   $181.75   $181.80  
  Purchase #6 $23.44   13.616%   $26.6316   $26.63   $26.65   $26.60  
  Purchase #7 $39.79   8.537%   $43.1869   $43.19   $43.20   $43.20  
  7 purchase totals = $629.12       $704.1381   $704.14   $704.15   $704.10