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 $186.79   8.467%   $202.6055   $202.61   $202.60   $202.60  
  Purchase #2 $158.43   13.400%   $179.6596   $179.66   $179.65   $179.70  
  Purchase #3 $61.27   4.849%   $64.241   $64.24   $64.25   $64.20  
  Purchase #4 $49.68   13.154%   $56.2149   $56.21   $56.20   $56.20  
  Purchase #5 $110.93   13.405%   $125.8002   $125.80   $125.80   $125.80  
  Purchase #6 $138.37   11.506%   $154.2909   $154.29   $154.30   $154.30  
  Purchase #7 $226.49   8.680%   $246.1493   $246.15   $246.15   $246.10  
  7 purchase totals = $931.96       $1,028.9614   $1,028.96   $1,028.95   $1,028.90