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 $57.55   12.255%   $64.6028   $64.60   $64.60   $64.60  
  Purchase #2 $160.56   9.376%   $175.6141   $175.61   $175.60   $175.60  
  Purchase #3 $138.94   11.794%   $155.3266   $155.33   $155.35   $155.30  
  Purchase #4 $239.46   13.435%   $271.6315   $271.63   $271.65   $271.60  
  Purchase #5 $106.45   5.226%   $112.0131   $112.01   $112.00   $112.00  
  Purchase #6 $243.62   6.486%   $259.4212   $259.42   $259.40   $259.40  
  Purchase #7 $53.28   6.428%   $56.7048   $56.70   $56.70   $56.70  
  7 purchase totals = $999.86       $1,095.3141   $1,095.30   $1,095.30   $1,095.20