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 $92.47   3.594%   $95.7934   $95.79   $95.80   $95.80  
  Purchase #2 $223.48   12.349%   $251.0775   $251.08   $251.10   $251.10  
  Purchase #3 $55.43   9.526%   $60.7103   $60.71   $60.70   $60.70  
  Purchase #4 $85.66   6.258%   $91.0206   $91.02   $91.00   $91.00  
  Purchase #5 $182.77   13.771%   $207.9393   $207.94   $207.95   $207.90  
  Purchase #6 $235.74   7.552%   $253.5431   $253.54   $253.55   $253.50  
  Purchase #7 $122.93   5.133%   $129.24   $129.24   $129.25   $129.20  
  7 purchase totals = $998.48       $1,089.3242   $1,089.32   $1,089.35   $1,089.20