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 $94.44   3.288%   $97.5452   $97.55   $97.55   $97.50  
  Purchase #2 $114.36   5.123%   $120.2187   $120.22   $120.20   $120.20  
  Purchase #3 $168.93   11.481%   $188.3249   $188.32   $188.30   $188.30  
  Purchase #4 $226.52   8.487%   $245.7448   $245.74   $245.75   $245.70  
  Purchase #5 $23.84   13.837%   $27.1387   $27.14   $27.15   $27.10  
  Purchase #6 $171.67   12.458%   $193.0566   $193.06   $193.05   $193.10  
  Purchase #7 $183.77   5.724%   $194.289   $194.29   $194.30   $194.30  
  7 purchase totals = $983.53       $1,066.3179   $1,066.32   $1,066.30   $1,066.20