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 $93.29   12.275%   $104.7413   $104.74   $104.75   $104.70  
  Purchase #2 $87.25   12.715%   $98.3438   $98.34   $98.35   $98.30  
  Purchase #3 $9.68   11.707%   $10.8132   $10.81   $10.80   $10.80  
  Purchase #4 $23.41   4.822%   $24.5388   $24.54   $24.55   $24.50  
  Purchase #5 $141.76   8.495%   $153.8025   $153.80   $153.80   $153.80  
  Purchase #6 $249.97   13.435%   $283.5535   $283.55   $283.55   $283.60  
  Purchase #7 $114.54   7.664%   $123.3183   $123.32   $123.30   $123.30  
  7 purchase totals = $719.90       $799.1114   $799.10   $799.10   $799.00