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 $31.69   6.474%   $33.7416   $33.74   $33.75   $33.70  
  Purchase #2 $147.31   4.636%   $154.1393   $154.14   $154.15   $154.10  
  Purchase #3 $122.89   5.263%   $129.3577   $129.36   $129.35   $129.40  
  Purchase #4 $238.34   3.167%   $245.8882   $245.89   $245.90   $245.90  
  Purchase #5 $43.97   6.443%   $46.803   $46.80   $46.80   $46.80  
  Purchase #6 $192.61   3.774%   $199.8791   $199.88   $199.90   $199.90  
  Purchase #7 $65.68   13.174%   $74.3327   $74.33   $74.35   $74.30  
  7 purchase totals = $842.49       $884.1416   $884.14   $884.20   $884.10