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 $243.77   8.396%   $264.2369   $264.24   $264.25   $264.20  
  Purchase #2 $170.45   13.465%   $193.4011   $193.40   $193.40   $193.40  
  Purchase #3 $10.52   10.162%   $11.589   $11.59   $11.60   $11.60  
  Purchase #4 $194.25   5.657%   $205.2387   $205.24   $205.25   $205.20  
  Purchase #5 $146.47   5.779%   $154.9345   $154.93   $154.95   $154.90  
  Purchase #6 $185.49   12.672%   $208.9953   $209.00   $209.00   $209.00  
  Purchase #7 $148.88   10.642%   $164.7238   $164.72   $164.70   $164.70  
  7 purchase totals = $1,099.83       $1,203.1193   $1,203.12   $1,203.15   $1,203.00