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 $201.79   8.822%   $219.5919   $219.59   $219.60   $219.60  
  Purchase #2 $21.75   11.227%   $24.1919   $24.19   $24.20   $24.20  
  Purchase #3 $5.92   10.717%   $6.5544   $6.55   $6.55   $6.60  
  Purchase #4 $233.31   4.136%   $242.9597   $242.96   $242.95   $243.00  
  Purchase #5 $131.79   12.156%   $147.8104   $147.81   $147.80   $147.80  
  Purchase #6 $122.78   7.730%   $132.2709   $132.27   $132.25   $132.30  
  Purchase #7 $188.29   8.110%   $203.5603   $203.56   $203.55   $203.60  
  7 purchase totals = $905.63       $976.9395   $976.93   $976.90   $977.10