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 $55.31   8.445%   $59.9809   $59.98   $60.00   $60.00  
  Purchase #2 $222.29   8.702%   $241.6337   $241.63   $241.65   $241.60  
  Purchase #3 $110.63   3.432%   $114.4268   $114.43   $114.45   $114.40  
  Purchase #4 $46.47   12.451%   $52.256   $52.26   $52.25   $52.30  
  Purchase #5 $130.44   5.767%   $137.9625   $137.96   $137.95   $138.00  
  Purchase #6 $66.87   11.383%   $74.4818   $74.48   $74.50   $74.50  
  Purchase #7 $200.28   11.369%   $223.0498   $223.05   $223.05   $223.00  
  7 purchase totals = $832.29       $903.7915   $903.79   $903.85   $903.80