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 $57.74   6.222%   $61.3326   $61.33   $61.35   $61.30  
  Purchase #2 $53.84   13.226%   $60.9609   $60.96   $60.95   $61.00  
  Purchase #3 $84.70   8.606%   $91.9893   $91.99   $92.00   $92.00  
  Purchase #4 $191.45   12.573%   $215.521   $215.52   $215.50   $215.50  
  Purchase #5 $116.65   4.693%   $122.1244   $122.12   $122.10   $122.10  
  Purchase #6 $218.84   4.870%   $229.4975   $229.50   $229.50   $229.50  
  Purchase #7 $57.88   6.300%   $61.5264   $61.53   $61.55   $61.50  
  7 purchase totals = $781.10       $842.9521   $842.95   $842.95   $842.90