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 $180.25   13.811%   $205.1443   $205.14   $205.15   $205.10  
  Purchase #2 $250.73   13.701%   $285.0825   $285.08   $285.10   $285.10  
  Purchase #3 $68.56   9.197%   $74.8655   $74.87   $74.85   $74.90  
  Purchase #4 $32.84   3.169%   $33.8807   $33.88   $33.90   $33.90  
  Purchase #5 $50.88   13.290%   $57.642   $57.64   $57.65   $57.60  
  Purchase #6 $80.77   6.377%   $85.9207   $85.92   $85.90   $85.90  
  Purchase #7 $27.75   6.305%   $29.4996   $29.50   $29.50   $29.50  
  7 purchase totals = $691.78       $772.0353   $772.03   $772.05   $772.00