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 $52.30   11.117%   $58.1142   $58.11   $58.10   $58.10  
  Purchase #2 $183.81   11.344%   $204.6614   $204.66   $204.65   $204.70  
  Purchase #3 $26.44   6.675%   $28.2049   $28.20   $28.20   $28.20  
  Purchase #4 $193.28   10.685%   $213.932   $213.93   $213.95   $213.90  
  Purchase #5 $118.25   6.182%   $125.5602   $125.56   $125.55   $125.60  
  Purchase #6 $169.82   7.529%   $182.6057   $182.61   $182.60   $182.60  
  Purchase #7 $174.80   12.442%   $196.5486   $196.55   $196.55   $196.50  
  7 purchase totals = $918.70       $1,009.6270   $1,009.62   $1,009.60   $1,009.60