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 $49.84   6.248%   $52.954   $52.95   $52.95   $53.00  
  Purchase #2 $89.63   12.246%   $100.6061   $100.61   $100.60   $100.60  
  Purchase #3 $152.51   6.468%   $162.3743   $162.37   $162.35   $162.40  
  Purchase #4 $176.44   12.747%   $198.9308   $198.93   $198.95   $198.90  
  Purchase #5 $233.95   8.191%   $253.1128   $253.11   $253.10   $253.10  
  Purchase #6 $211.54   6.564%   $225.4255   $225.43   $225.45   $225.40  
  Purchase #7 $202.33   10.692%   $223.9631   $223.96   $223.95   $224.00  
  7 purchase totals = $1,116.24       $1,217.3666   $1,217.36   $1,217.35   $1,217.40