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 $58.31   11.797%   $65.1888   $65.19   $65.20   $65.20  
  Purchase #2 $89.63   8.622%   $97.3579   $97.36   $97.35   $97.40  
  Purchase #3 $180.85   4.631%   $189.2252   $189.23   $189.25   $189.20  
  Purchase #4 $224.48   3.270%   $231.8205   $231.82   $231.80   $231.80  
  Purchase #5 $247.95   12.248%   $278.3189   $278.32   $278.30   $278.30  
  Purchase #6 $233.75   8.218%   $252.9596   $252.96   $252.95   $253.00  
  Purchase #7 $14.52   12.643%   $16.3558   $16.36   $16.35   $16.40  
  7 purchase totals = $1,049.49       $1,131.2267   $1,131.24   $1,131.20   $1,131.30