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 $162.83   11.119%   $180.9351   $180.94   $180.95   $180.90  
  Purchase #2 $225.91   6.779%   $241.2244   $241.22   $241.20   $241.20  
  Purchase #3 $146.27   12.332%   $164.308   $164.31   $164.30   $164.30  
  Purchase #4 $113.51   11.164%   $126.1823   $126.18   $126.20   $126.20  
  Purchase #5 $212.68   10.492%   $234.9944   $234.99   $235.00   $235.00  
  Purchase #6 $57.52   5.207%   $60.5151   $60.52   $60.50   $60.50  
  Purchase #7 $131.80   3.570%   $136.5053   $136.51   $136.50   $136.50  
  7 purchase totals = $1,050.52       $1,144.6646   $1,144.67   $1,144.65   $1,144.60