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 $36.94   11.229%   $41.088   $41.09   $41.10   $41.10  
  Purchase #2 $65.46   13.201%   $74.1014   $74.10   $74.10   $74.10  
  Purchase #3 $201.25   9.104%   $219.5718   $219.57   $219.55   $219.60  
  Purchase #4 $209.93   12.675%   $236.5386   $236.54   $236.55   $236.50  
  Purchase #5 $217.47   13.325%   $246.4479   $246.45   $246.45   $246.40  
  Purchase #6 $85.54   10.162%   $94.2326   $94.23   $94.25   $94.20  
  Purchase #7 $109.59   13.661%   $124.5611   $124.56   $124.55   $124.60  
  7 purchase totals = $926.18       $1,036.5414   $1,036.54   $1,036.55   $1,036.50