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 $29.55   10.155%   $32.5508   $32.55   $32.55   $32.60  
  Purchase #2 $69.28   9.267%   $75.7002   $75.70   $75.70   $75.70  
  Purchase #3 $47.47   13.144%   $53.7095   $53.71   $53.70   $53.70  
  Purchase #4 $36.87   11.183%   $40.9932   $40.99   $41.00   $41.00  
  Purchase #5 $152.78   6.402%   $162.561   $162.56   $162.55   $162.60  
  Purchase #6 $173.82   3.710%   $180.2687   $180.27   $180.25   $180.30  
  Purchase #7 $166.83   8.824%   $181.5511   $181.55   $181.55   $181.60  
  7 purchase totals = $676.60       $727.3345   $727.33   $727.30   $727.50