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 $85.92   8.654%   $93.3555   $93.36   $93.35   $93.40  
  Purchase #2 $187.83   13.395%   $212.9898   $212.99   $213.00   $213.00  
  Purchase #3 $151.67   6.438%   $161.4345   $161.43   $161.45   $161.40  
  Purchase #4 $99.61   7.145%   $106.7271   $106.73   $106.75   $106.70  
  Purchase #5 $49.85   12.233%   $55.9482   $55.95   $55.95   $55.90  
  Purchase #6 $212.64   4.216%   $221.6049   $221.60   $221.60   $221.60  
  Purchase #7 $145.95   9.240%   $159.4358   $159.44   $159.45   $159.40  
  7 purchase totals = $933.47       $1,011.4958   $1,011.50   $1,011.55   $1,011.40