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 $62.47   8.375%   $67.7019   $67.70   $67.70   $67.70  
  Purchase #2 $201.42   4.537%   $210.5584   $210.56   $210.55   $210.60  
  Purchase #3 $188.47   11.454%   $210.0574   $210.06   $210.05   $210.10  
  Purchase #4 $109.98   10.258%   $121.2617   $121.26   $121.25   $121.30  
  Purchase #5 $34.34   10.626%   $37.989   $37.99   $38.00   $38.00  
  Purchase #6 $139.66   9.793%   $153.3369   $153.34   $153.35   $153.30  
  Purchase #7 $207.66   8.191%   $224.6694   $224.67   $224.65   $224.70  
  7 purchase totals = $944.00       $1,025.5747   $1,025.58   $1,025.55   $1,025.70