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 $32.93   6.172%   $34.9624   $34.96   $34.95   $35.00  
  Purchase #2 $175.28   3.154%   $180.8083   $180.81   $180.80   $180.80  
  Purchase #3 $109.75   9.241%   $119.892   $119.89   $119.90   $119.90  
  Purchase #4 $245.77   4.514%   $256.8641   $256.86   $256.85   $256.90  
  Purchase #5 $63.52   3.538%   $65.7673   $65.77   $65.75   $65.80  
  Purchase #6 $173.64   10.205%   $191.36   $191.36   $191.35   $191.40  
  Purchase #7 $7.94   7.142%   $8.5071   $8.51   $8.50   $8.50  
  7 purchase totals = $808.83       $858.1612   $858.16   $858.10   $858.30