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 $78.91   6.822%   $84.2932   $84.29   $84.30   $84.30  
  Purchase #2 $101.30   12.504%   $113.9666   $113.97   $113.95   $114.00  
  Purchase #3 $32.31   8.379%   $35.0173   $35.02   $35.00   $35.00  
  Purchase #4 $245.41   9.746%   $269.3277   $269.33   $269.35   $269.30  
  Purchase #5 $180.67   6.507%   $192.4262   $192.43   $192.45   $192.40  
  Purchase #6 $106.95   3.522%   $110.7168   $110.72   $110.70   $110.70  
  Purchase #7 $204.53   9.252%   $223.4531   $223.45   $223.45   $223.50  
  7 purchase totals = $950.08       $1,029.2009   $1,029.21   $1,029.20   $1,029.20