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 $184.77   10.819%   $204.7603   $204.76   $204.75   $204.80  
  Purchase #2 $198.79   6.497%   $211.7054   $211.71   $211.70   $211.70  
  Purchase #3 $27.80   3.488%   $28.7697   $28.77   $28.75   $28.80  
  Purchase #4 $223.54   7.277%   $239.807   $239.81   $239.80   $239.80  
  Purchase #5 $72.80   9.851%   $79.9715   $79.97   $79.95   $80.00  
  Purchase #6 $98.35   13.444%   $111.5722   $111.57   $111.55   $111.60  
  Purchase #7 $200.38   8.351%   $217.1137   $217.11   $217.10   $217.10  
  7 purchase totals = $1,006.43       $1,093.6998   $1,093.70   $1,093.60   $1,093.80