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 $71.29   7.409%   $76.5719   $76.57   $76.55   $76.60  
  Purchase #2 $225.73   6.786%   $241.048   $241.05   $241.05   $241.00  
  Purchase #3 $44.47   3.584%   $46.0638   $46.06   $46.05   $46.10  
  Purchase #4 $34.39   8.299%   $37.244   $37.24   $37.25   $37.20  
  Purchase #5 $68.52   12.661%   $77.1953   $77.20   $77.20   $77.20  
  Purchase #6 $204.71   7.298%   $219.6497   $219.65   $219.65   $219.60  
  Purchase #7 $147.43   7.356%   $158.275   $158.28   $158.30   $158.30  
  7 purchase totals = $796.54       $856.0477   $856.05   $856.05   $856.00