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 $147.25   11.803%   $164.6299   $164.63   $164.65   $164.60  
  Purchase #2 $21.41   11.782%   $23.9325   $23.93   $23.95   $23.90  
  Purchase #3 $17.65   10.306%   $19.469   $19.47   $19.45   $19.50  
  Purchase #4 $58.29   8.466%   $63.2248   $63.22   $63.20   $63.20  
  Purchase #5 $64.91   9.319%   $70.959   $70.96   $70.95   $71.00  
  Purchase #6 $87.49   10.611%   $96.7736   $96.77   $96.75   $96.80  
  Purchase #7 $235.69   11.717%   $263.3058   $263.31   $263.30   $263.30  
  7 purchase totals = $632.69       $702.2946   $702.29   $702.25   $702.30