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 $53.45   7.318%   $57.3615   $57.36   $57.35   $57.40  
  Purchase #2 $190.52   4.721%   $199.5144   $199.51   $199.50   $199.50  
  Purchase #3 $177.52   9.143%   $193.7507   $193.75   $193.75   $193.80  
  Purchase #4 $22.50   6.563%   $23.9767   $23.98   $24.00   $24.00  
  Purchase #5 $177.80   13.661%   $202.0893   $202.09   $202.10   $202.10  
  Purchase #6 $241.42   5.421%   $254.5074   $254.51   $254.50   $254.50  
  Purchase #7 $127.56   4.274%   $133.0119   $133.01   $133.00   $133.00  
  7 purchase totals = $990.77       $1,064.2119   $1,064.21   $1,064.20   $1,064.30