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 $60.48   8.570%   $65.6631   $65.66   $65.65   $65.70  
  Purchase #2 $247.98   9.270%   $270.9677   $270.97   $270.95   $271.00  
  Purchase #3 $210.72   13.634%   $239.4496   $239.45   $239.45   $239.40  
  Purchase #4 $176.69   11.805%   $197.5483   $197.55   $197.55   $197.50  
  Purchase #5 $84.55   11.793%   $94.521   $94.52   $94.50   $94.50  
  Purchase #6 $214.32   5.235%   $225.5397   $225.54   $225.55   $225.50  
  Purchase #7 $185.58   8.667%   $201.6642   $201.66   $201.65   $201.70  
  7 purchase totals = $1,180.32       $1,295.3536   $1,295.35   $1,295.30   $1,295.30