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 $175.87   13.219%   $199.1183   $199.12   $199.10   $199.10  
  Purchase #2 $53.67   3.276%   $55.4282   $55.43   $55.45   $55.40  
  Purchase #3 $79.62   7.584%   $85.6584   $85.66   $85.65   $85.70  
  Purchase #4 $35.77   4.247%   $37.2892   $37.29   $37.30   $37.30  
  Purchase #5 $232.57   8.690%   $252.7803   $252.78   $252.80   $252.80  
  Purchase #6 $5.74   10.132%   $6.3216   $6.32   $6.30   $6.30  
  Purchase #7 $14.96   8.338%   $16.2074   $16.21   $16.20   $16.20  
  7 purchase totals = $598.20       $652.8034   $652.81   $652.80   $652.80