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 $84.47   12.367%   $94.9164   $94.92   $94.90   $94.90  
  Purchase #2 $197.87   6.498%   $210.7276   $210.73   $210.75   $210.70  
  Purchase #3 $35.47   6.463%   $37.7624   $37.76   $37.75   $37.80  
  Purchase #4 $222.74   8.313%   $241.2564   $241.26   $241.25   $241.30  
  Purchase #5 $69.26   9.666%   $75.9547   $75.95   $75.95   $76.00  
  Purchase #6 $174.81   5.392%   $184.2358   $184.24   $184.25   $184.20  
  Purchase #7 $210.47   7.713%   $226.7036   $226.70   $226.70   $226.70  
  7 purchase totals = $995.09       $1,071.5569   $1,071.56   $1,071.55   $1,071.60