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 $43.81   13.238%   $49.6096   $49.61   $49.60   $49.60  
  Purchase #2 $93.61   9.655%   $102.648   $102.65   $102.65   $102.60  
  Purchase #3 $156.62   13.379%   $177.5742   $177.57   $177.55   $177.60  
  Purchase #4 $153.69   11.464%   $171.309   $171.31   $171.30   $171.30  
  Purchase #5 $186.46   8.142%   $201.6416   $201.64   $201.65   $201.60  
  Purchase #6 $68.34   3.322%   $70.6103   $70.61   $70.60   $70.60  
  Purchase #7 $91.76   5.715%   $97.0041   $97.00   $97.00   $97.00  
  7 purchase totals = $794.29       $870.3968   $870.39   $870.35   $870.30