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 $100.65   8.348%   $109.0523   $109.05   $109.05   $109.10  
  Purchase #2 $205.93   12.783%   $232.254   $232.25   $232.25   $232.30  
  Purchase #3 $200.94   8.546%   $218.1123   $218.11   $218.10   $218.10  
  Purchase #4 $143.76   11.416%   $160.1716   $160.17   $160.15   $160.20  
  Purchase #5 $141.71   6.263%   $150.5853   $150.59   $150.60   $150.60  
  Purchase #6 $191.56   7.504%   $205.9347   $205.93   $205.95   $205.90  
  Purchase #7 $140.61   6.213%   $149.3461   $149.35   $149.35   $149.30  
  7 purchase totals = $1,125.16       $1,225.4563   $1,225.45   $1,225.45   $1,225.50