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 $212.88   9.616%   $233.3505   $233.35   $233.35   $233.40  
  Purchase #2 $118.59   13.384%   $134.4621   $134.46   $134.45   $134.50  
  Purchase #3 $147.90   3.739%   $153.43   $153.43   $153.45   $153.40  
  Purchase #4 $168.73   5.495%   $178.0017   $178.00   $178.00   $178.00  
  Purchase #5 $83.36   10.132%   $91.806   $91.81   $91.80   $91.80  
  Purchase #6 $193.44   4.570%   $202.2802   $202.28   $202.30   $202.30  
  Purchase #7 $60.34   9.741%   $66.2177   $66.22   $66.20   $66.20  
  7 purchase totals = $985.24       $1,059.5482   $1,059.55   $1,059.55   $1,059.60