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 $206.26   12.640%   $232.3313   $232.33   $232.35   $232.30  
  Purchase #2 $33.81   4.533%   $35.3426   $35.34   $35.35   $35.30  
  Purchase #3 $124.58   4.118%   $129.7102   $129.71   $129.70   $129.70  
  Purchase #4 $147.60   10.539%   $163.1556   $163.16   $163.15   $163.20  
  Purchase #5 $203.53   11.560%   $227.0581   $227.06   $227.05   $227.10  
  Purchase #6 $220.75   11.443%   $246.0104   $246.01   $246.00   $246.00  
  Purchase #7 $232.82   13.580%   $264.437   $264.44   $264.45   $264.40  
  7 purchase totals = $1,169.35       $1,298.0452   $1,298.05   $1,298.05   $1,298.00