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 $58.70   7.356%   $63.018   $63.02   $63.00   $63.00  
  Purchase #2 $50.27   12.816%   $56.7126   $56.71   $56.70   $56.70  
  Purchase #3 $241.27   7.545%   $259.4738   $259.47   $259.45   $259.50  
  Purchase #4 $37.65   10.494%   $41.601   $41.60   $41.60   $41.60  
  Purchase #5 $89.68   5.708%   $94.7989   $94.80   $94.80   $94.80  
  Purchase #6 $211.93   10.255%   $233.6634   $233.66   $233.65   $233.70  
  Purchase #7 $226.28   8.452%   $245.4052   $245.41   $245.40   $245.40  
  7 purchase totals = $915.78       $994.6729   $994.67   $994.60   $994.70