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 $202.98   10.812%   $224.9262   $224.93   $224.95   $224.90  
  Purchase #2 $69.39   5.288%   $73.0593   $73.06   $73.05   $73.10  
  Purchase #3 $167.98   10.394%   $185.4398   $185.44   $185.45   $185.40  
  Purchase #4 $235.93   12.235%   $264.796   $264.80   $264.80   $264.80  
  Purchase #5 $94.76   11.137%   $105.3134   $105.31   $105.30   $105.30  
  Purchase #6 $162.74   3.174%   $167.9054   $167.91   $167.90   $167.90  
  Purchase #7 $12.60   11.144%   $14.0041   $14.00   $14.00   $14.00  
  7 purchase totals = $946.38       $1,035.4442   $1,035.45   $1,035.45   $1,035.40