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 $181.63   12.234%   $203.8506   $203.85   $203.85   $203.90  
  Purchase #2 $79.80   9.820%   $87.6364   $87.64   $87.65   $87.60  
  Purchase #3 $56.90   4.663%   $59.5532   $59.55   $59.55   $59.60  
  Purchase #4 $155.76   10.871%   $172.6927   $172.69   $172.70   $172.70  
  Purchase #5 $112.35   11.571%   $125.35   $125.35   $125.35   $125.40  
  Purchase #6 $228.26   11.575%   $254.6811   $254.68   $254.70   $254.70  
  Purchase #7 $168.27   12.208%   $188.8124   $188.81   $188.80   $188.80  
  7 purchase totals = $982.97       $1,092.5764   $1,092.57   $1,092.60   $1,092.70