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 $104.35   11.162%   $115.9975   $116.00   $116.00   $116.00  
  Purchase #2 $160.94   12.599%   $181.2168   $181.22   $181.20   $181.20  
  Purchase #3 $39.93   11.365%   $44.468   $44.47   $44.45   $44.50  
  Purchase #4 $95.75   4.332%   $99.8979   $99.90   $99.90   $99.90  
  Purchase #5 $241.40   9.823%   $265.1127   $265.11   $265.10   $265.10  
  Purchase #6 $207.86   12.211%   $233.2418   $233.24   $233.25   $233.20  
  Purchase #7 $60.36   6.249%   $64.1319   $64.13   $64.15   $64.10  
  7 purchase totals = $910.59       $1,004.0666   $1,004.07   $1,004.05   $1,004.00