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 $65.43   7.272%   $70.1881   $70.19   $70.20   $70.20  
  Purchase #2 $229.83   9.493%   $251.6478   $251.65   $251.65   $251.60  
  Purchase #3 $6.57   10.609%   $7.267   $7.27   $7.25   $7.30  
  Purchase #4 $240.88   13.217%   $272.7171   $272.72   $272.70   $272.70  
  Purchase #5 $42.46   10.437%   $46.8916   $46.89   $46.90   $46.90  
  Purchase #6 $30.26   5.808%   $32.0175   $32.02   $32.00   $32.00  
  Purchase #7 $128.51   13.276%   $145.571   $145.57   $145.55   $145.60  
  7 purchase totals = $743.94       $826.3001   $826.31   $826.25   $826.30