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 $200.63   12.235%   $225.1771   $225.18   $225.20   $225.20  
  Purchase #2 $150.95   7.524%   $162.3075   $162.31   $162.30   $162.30  
  Purchase #3 $5.33   11.491%   $5.9425   $5.94   $5.95   $5.90  
  Purchase #4 $184.68   12.587%   $207.9257   $207.93   $207.95   $207.90  
  Purchase #5 $59.36   5.780%   $62.791   $62.79   $62.80   $62.80  
  Purchase #6 $187.72   8.553%   $203.7757   $203.78   $203.80   $203.80  
  Purchase #7 $145.49   6.226%   $154.5482   $154.55   $154.55   $154.50  
  7 purchase totals = $934.16       $1,022.4677   $1,022.48   $1,022.55   $1,022.40