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 $241.84   8.826%   $263.1848   $263.18   $263.20   $263.20  
  Purchase #2 $145.55   9.607%   $159.533   $159.53   $159.55   $159.50  
  Purchase #3 $127.84   5.606%   $135.0067   $135.01   $135.00   $135.00  
  Purchase #4 $66.55   11.707%   $74.341   $74.34   $74.35   $74.30  
  Purchase #5 $246.35   4.227%   $256.7632   $256.76   $256.75   $256.80  
  Purchase #6 $105.61   13.213%   $119.5642   $119.56   $119.55   $119.60  
  Purchase #7 $7.77   3.211%   $8.0195   $8.02   $8.00   $8.00  
  7 purchase totals = $941.51       $1,016.4124   $1,016.40   $1,016.40   $1,016.40