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 $169.78   11.690%   $189.6273   $189.63   $189.65   $189.60  
  Purchase #2 $53.55   12.695%   $60.3482   $60.35   $60.35   $60.30  
  Purchase #3 $126.57   9.393%   $138.4587   $138.46   $138.45   $138.50  
  Purchase #4 $249.32   9.280%   $272.4569   $272.46   $272.45   $272.50  
  Purchase #5 $185.97   10.743%   $205.9488   $205.95   $205.95   $205.90  
  Purchase #6 $140.65   11.352%   $156.6166   $156.62   $156.60   $156.60  
  Purchase #7 $186.74   8.597%   $202.794   $202.79   $202.80   $202.80  
  7 purchase totals = $1,112.58       $1,226.2505   $1,226.26   $1,226.25   $1,226.20