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 $61.87   11.628%   $69.0642   $69.06   $69.05   $69.10  
  Purchase #2 $232.93   13.349%   $264.0238   $264.02   $264.00   $264.00  
  Purchase #3 $44.52   11.340%   $49.5686   $49.57   $49.55   $49.60  
  Purchase #4 $156.27   9.656%   $171.3594   $171.36   $171.35   $171.40  
  Purchase #5 $84.57   9.730%   $92.7987   $92.80   $92.80   $92.80  
  Purchase #6 $8.98   10.735%   $9.944   $9.94   $9.95   $9.90  
  Purchase #7 $124.63   5.648%   $131.6691   $131.67   $131.65   $131.70  
  7 purchase totals = $713.77       $788.4278   $788.42   $788.35   $788.50