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 $70.61   4.118%   $73.5177   $73.52   $73.50   $73.50  
  Purchase #2 $206.60   3.498%   $213.8269   $213.83   $213.85   $213.80  
  Purchase #3 $106.34   11.474%   $118.5415   $118.54   $118.55   $118.50  
  Purchase #4 $38.27   9.793%   $42.0178   $42.02   $42.00   $42.00  
  Purchase #5 $176.80   6.402%   $188.1187   $188.12   $188.10   $188.10  
  Purchase #6 $222.94   3.548%   $230.8499   $230.85   $230.85   $230.80  
  Purchase #7 $10.60   6.655%   $11.3054   $11.31   $11.30   $11.30  
  7 purchase totals = $832.16       $878.1779   $878.19   $878.15   $878.00