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 $214.35   12.708%   $241.5896   $241.59   $241.60   $241.60  
  Purchase #2 $20.73   7.767%   $22.3401   $22.34   $22.35   $22.30  
  Purchase #3 $5.32   12.457%   $5.9827   $5.98   $6.00   $6.00  
  Purchase #4 $144.29   6.584%   $153.7901   $153.79   $153.80   $153.80  
  Purchase #5 $226.83   5.107%   $238.4142   $238.41   $238.40   $238.40  
  Purchase #6 $181.83   10.527%   $200.9712   $200.97   $200.95   $201.00  
  Purchase #7 $97.99   8.807%   $106.62   $106.62   $106.60   $106.60  
  7 purchase totals = $891.34       $969.7079   $969.70   $969.70   $969.70