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 $173.38   13.323%   $196.4794   $196.48   $196.50   $196.50  
  Purchase #2 $190.29   6.150%   $201.9928   $201.99   $202.00   $202.00  
  Purchase #3 $114.35   9.825%   $125.5849   $125.58   $125.60   $125.60  
  Purchase #4 $163.33   12.280%   $183.3869   $183.39   $183.40   $183.40  
  Purchase #5 $96.52   3.224%   $99.6318   $99.63   $99.65   $99.60  
  Purchase #6 $247.38   6.202%   $262.7225   $262.72   $262.70   $262.70  
  Purchase #7 $226.85   3.180%   $234.0638   $234.06   $234.05   $234.10  
  7 purchase totals = $1,212.10       $1,303.8621   $1,303.85   $1,303.90   $1,303.90