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 $217.96   13.216%   $246.7656   $246.77   $246.75   $246.80  
  Purchase #2 $198.31   5.627%   $209.4689   $209.47   $209.45   $209.50  
  Purchase #3 $236.81   4.765%   $248.094   $248.09   $248.10   $248.10  
  Purchase #4 $240.81   9.435%   $263.5304   $263.53   $263.55   $263.50  
  Purchase #5 $43.25   8.723%   $47.0227   $47.02   $47.00   $47.00  
  Purchase #6 $32.79   5.823%   $34.6994   $34.70   $34.70   $34.70  
  Purchase #7 $61.72   5.466%   $65.0936   $65.09   $65.10   $65.10  
  7 purchase totals = $1,031.65       $1,114.6746   $1,114.67   $1,114.65   $1,114.70