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 $32.74   5.850%   $34.6553   $34.66   $34.65   $34.70  
  Purchase #2 $118.56   13.191%   $134.1992   $134.20   $134.20   $134.20  
  Purchase #3 $151.67   5.847%   $160.5381   $160.54   $160.55   $160.50  
  Purchase #4 $28.47   4.563%   $29.7691   $29.77   $29.75   $29.80  
  Purchase #5 $7.40   12.108%   $8.296   $8.30   $8.30   $8.30  
  Purchase #6 $76.37   10.402%   $84.314   $84.31   $84.30   $84.30  
  Purchase #7 $225.27   7.242%   $241.5841   $241.58   $241.60   $241.60  
  7 purchase totals = $640.48       $693.3558   $693.36   $693.35   $693.40