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 $94.97   12.708%   $107.0388   $107.04   $107.05   $107.00  
  Purchase #2 $181.91   11.381%   $202.6132   $202.61   $202.60   $202.60  
  Purchase #3 $9.67   12.141%   $10.844   $10.84   $10.85   $10.80  
  Purchase #4 $153.27   6.562%   $163.3276   $163.33   $163.35   $163.30  
  Purchase #5 $64.83   3.770%   $67.2741   $67.27   $67.25   $67.30  
  Purchase #6 $159.72   10.308%   $176.1839   $176.18   $176.20   $176.20  
  Purchase #7 $202.95   3.731%   $210.5221   $210.52   $210.50   $210.50  
  7 purchase totals = $867.32       $937.8037   $937.79   $937.80   $937.70