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 $32.52   3.580%   $33.6842   $33.68   $33.70   $33.70  
  Purchase #2 $119.82   13.803%   $136.3588   $136.36   $136.35   $136.40  
  Purchase #3 $99.95   6.493%   $106.4398   $106.44   $106.45   $106.40  
  Purchase #4 $148.55   10.340%   $163.9101   $163.91   $163.90   $163.90  
  Purchase #5 $101.68   11.274%   $113.1434   $113.14   $113.15   $113.10  
  Purchase #6 $182.27   12.160%   $204.434   $204.43   $204.45   $204.40  
  Purchase #7 $106.95   9.403%   $117.0065   $117.01   $117.00   $117.00  
  7 purchase totals = $791.74       $874.9768   $874.97   $875.00   $874.90