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 $60.78   11.126%   $67.5424   $67.54   $67.55   $67.50  
  Purchase #2 $172.98   11.683%   $193.1893   $193.19   $193.20   $193.20  
  Purchase #3 $33.89   4.553%   $35.433   $35.43   $35.45   $35.40  
  Purchase #4 $52.78   6.248%   $56.0777   $56.08   $56.10   $56.10  
  Purchase #5 $86.79   11.818%   $97.0468   $97.05   $97.05   $97.00  
  Purchase #6 $236.94   13.301%   $268.4554   $268.46   $268.45   $268.50  
  Purchase #7 $231.58   6.833%   $247.4039   $247.40   $247.40   $247.40  
  7 purchase totals = $875.74       $965.1485   $965.15   $965.20   $965.10