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 $223.48   13.229%   $253.0442   $253.04   $253.05   $253.00  
  Purchase #2 $38.38   13.159%   $43.4304   $43.43   $43.45   $43.40  
  Purchase #3 $179.33   3.124%   $184.9323   $184.93   $184.95   $184.90  
  Purchase #4 $160.49   9.421%   $175.6098   $175.61   $175.60   $175.60  
  Purchase #5 $142.49   10.270%   $157.1237   $157.12   $157.10   $157.10  
  Purchase #6 $26.82   6.492%   $28.5612   $28.56   $28.55   $28.60  
  Purchase #7 $201.26   8.157%   $217.6768   $217.68   $217.70   $217.70  
  7 purchase totals = $972.25       $1,060.3784   $1,060.37   $1,060.40   $1,060.30