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 $60.94   11.836%   $68.1529   $68.15   $68.15   $68.20  
  Purchase #2 $55.71   5.349%   $58.6899   $58.69   $58.70   $58.70  
  Purchase #3 $160.40   9.518%   $175.6669   $175.67   $175.65   $175.70  
  Purchase #4 $29.26   10.523%   $32.339   $32.34   $32.35   $32.30  
  Purchase #5 $87.94   6.864%   $93.9762   $93.98   $94.00   $94.00  
  Purchase #6 $65.62   5.160%   $69.006   $69.01   $69.00   $69.00  
  Purchase #7 $160.88   9.530%   $176.2119   $176.21   $176.20   $176.20  
  7 purchase totals = $620.75       $674.0428   $674.05   $674.05   $674.10