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 $69.54   3.517%   $71.9857   $71.99   $72.00   $72.00  
  Purchase #2 $247.67   8.740%   $269.3164   $269.32   $269.30   $269.30  
  Purchase #3 $109.32   10.714%   $121.0325   $121.03   $121.05   $121.00  
  Purchase #4 $156.90   13.866%   $178.6558   $178.66   $178.65   $178.70  
  Purchase #5 $222.78   12.678%   $251.024   $251.02   $251.00   $251.00  
  Purchase #6 $46.58   12.364%   $52.3392   $52.34   $52.35   $52.30  
  Purchase #7 $123.87   5.220%   $130.336   $130.34   $130.35   $130.30  
  7 purchase totals = $976.66       $1,074.6896   $1,074.70   $1,074.70   $1,074.60