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 $149.98   7.770%   $161.6334   $161.63   $161.65   $161.60  
  Purchase #2 $241.74   4.398%   $252.3717   $252.37   $252.35   $252.40  
  Purchase #3 $58.99   9.629%   $64.6701   $64.67   $64.65   $64.70  
  Purchase #4 $53.29   4.288%   $55.5751   $55.58   $55.60   $55.60  
  Purchase #5 $48.98   12.775%   $55.2372   $55.24   $55.25   $55.20  
  Purchase #6 $203.67   4.295%   $212.4176   $212.42   $212.40   $212.40  
  Purchase #7 $229.84   3.683%   $238.305   $238.31   $238.30   $238.30  
  7 purchase totals = $986.49       $1,040.2101   $1,040.22   $1,040.20   $1,040.20