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 $83.32   12.765%   $93.9558   $93.96   $93.95   $94.00  
  Purchase #2 $218.26   10.220%   $240.5662   $240.57   $240.55   $240.60  
  Purchase #3 $131.42   11.408%   $146.4124   $146.41   $146.40   $146.40  
  Purchase #4 $186.38   10.584%   $206.1065   $206.11   $206.10   $206.10  
  Purchase #5 $37.93   12.479%   $42.6633   $42.66   $42.65   $42.70  
  Purchase #6 $229.96   4.405%   $240.0897   $240.09   $240.10   $240.10  
  Purchase #7 $70.81   12.585%   $79.7214   $79.72   $79.70   $79.70  
  7 purchase totals = $958.08       $1,049.5153   $1,049.52   $1,049.45   $1,049.60