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 $224.48   11.620%   $250.5646   $250.56   $250.55   $250.60  
  Purchase #2 $65.67   12.145%   $73.6456   $73.65   $73.65   $73.60  
  Purchase #3 $197.45   7.229%   $211.7237   $211.72   $211.70   $211.70  
  Purchase #4 $217.38   10.253%   $239.668   $239.67   $239.65   $239.70  
  Purchase #5 $232.83   13.359%   $263.9338   $263.93   $263.95   $263.90  
  Purchase #6 $245.81   7.559%   $264.3908   $264.39   $264.40   $264.40  
  Purchase #7 $120.89   5.281%   $127.2742   $127.27   $127.25   $127.30  
  7 purchase totals = $1,304.51       $1,431.2007   $1,431.19   $1,431.15   $1,431.20