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 $223.89   9.871%   $245.9902   $245.99   $246.00   $246.00  
  Purchase #2 $221.43   8.290%   $239.7865   $239.79   $239.80   $239.80  
  Purchase #3 $111.30   12.463%   $125.1713   $125.17   $125.15   $125.20  
  Purchase #4 $24.51   11.827%   $27.4088   $27.41   $27.40   $27.40  
  Purchase #5 $34.74   3.727%   $36.0348   $36.03   $36.05   $36.00  
  Purchase #6 $211.52   3.607%   $219.1495   $219.15   $219.15   $219.10  
  Purchase #7 $120.53   6.203%   $128.0065   $128.01   $128.00   $128.00  
  7 purchase totals = $947.92       $1,021.5476   $1,021.55   $1,021.55   $1,021.50