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 $86.78   6.340%   $92.2819   $92.28   $92.30   $92.30  
  Purchase #2 $246.27   4.750%   $257.9678   $257.97   $257.95   $258.00  
  Purchase #3 $136.37   10.362%   $150.5007   $150.50   $150.50   $150.50  
  Purchase #4 $187.99   6.655%   $200.5007   $200.50   $200.50   $200.50  
  Purchase #5 $38.89   4.423%   $40.6101   $40.61   $40.60   $40.60  
  Purchase #6 $57.74   11.751%   $64.525   $64.53   $64.55   $64.50  
  Purchase #7 $216.96   5.632%   $229.1792   $229.18   $229.20   $229.20  
  7 purchase totals = $971.00       $1,035.5654   $1,035.57   $1,035.60   $1,035.60