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 $196.61   3.162%   $202.8268   $202.83   $202.85   $202.80  
  Purchase #2 $174.29   9.341%   $190.5704   $190.57   $190.55   $190.60  
  Purchase #3 $34.56   9.873%   $37.9721   $37.97   $37.95   $38.00  
  Purchase #4 $230.72   11.509%   $257.2736   $257.27   $257.25   $257.30  
  Purchase #5 $9.42   12.290%   $10.5777   $10.58   $10.60   $10.60  
  Purchase #6 $123.30   13.808%   $140.3253   $140.33   $140.35   $140.30  
  Purchase #7 $123.27   9.742%   $135.279   $135.28   $135.30   $135.30  
  7 purchase totals = $892.17       $974.8249   $974.83   $974.85   $974.90