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 $129.84   9.599%   $142.3033   $142.30   $142.30   $142.30  
  Purchase #2 $15.39   7.680%   $16.572   $16.57   $16.55   $16.60  
  Purchase #3 $146.59   9.842%   $161.0174   $161.02   $161.00   $161.00  
  Purchase #4 $249.77   9.774%   $274.1825   $274.18   $274.20   $274.20  
  Purchase #5 $224.78   4.283%   $234.4073   $234.41   $234.40   $234.40  
  Purchase #6 $50.75   12.245%   $56.9643   $56.96   $56.95   $57.00  
  Purchase #7 $157.52   11.361%   $175.4158   $175.42   $175.40   $175.40  
  7 purchase totals = $974.64       $1,060.8626   $1,060.86   $1,060.80   $1,060.90