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 $242.61   4.476%   $253.4692   $253.47   $253.45   $253.50  
  Purchase #2 $209.41   12.820%   $236.2564   $236.26   $236.25   $236.30  
  Purchase #3 $175.30   7.523%   $188.4878   $188.49   $188.50   $188.50  
  Purchase #4 $156.26   12.623%   $175.9847   $175.98   $176.00   $176.00  
  Purchase #5 $43.52   3.368%   $44.9858   $44.99   $45.00   $45.00  
  Purchase #6 $232.39   12.760%   $262.043   $262.04   $262.05   $262.00  
  Purchase #7 $28.70   10.368%   $31.6756   $31.68   $31.70   $31.70  
  7 purchase totals = $1,088.19       $1,192.9025   $1,192.91   $1,192.95   $1,193.00