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 $183.37   10.801%   $203.1758   $203.18   $203.20   $203.20  
  Purchase #2 $215.93   5.629%   $228.0847   $228.08   $228.10   $228.10  
  Purchase #3 $178.49   4.569%   $186.6452   $186.65   $186.65   $186.60  
  Purchase #4 $45.27   12.625%   $50.9853   $50.99   $51.00   $51.00  
  Purchase #5 $192.70   8.599%   $209.2703   $209.27   $209.25   $209.30  
  Purchase #6 $131.76   10.610%   $145.7397   $145.74   $145.75   $145.70  
  Purchase #7 $33.76   12.608%   $38.0165   $38.02   $38.00   $38.00  
  7 purchase totals = $981.28       $1,061.9175   $1,061.93   $1,061.95   $1,061.90