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 $30.40   13.684%   $34.5599   $34.56   $34.55   $34.60  
  Purchase #2 $208.89   12.258%   $234.4957   $234.50   $234.50   $234.50  
  Purchase #3 $184.55   11.511%   $205.7936   $205.79   $205.80   $205.80  
  Purchase #4 $69.44   7.106%   $74.3744   $74.37   $74.35   $74.40  
  Purchase #5 $195.59   6.644%   $208.585   $208.59   $208.60   $208.60  
  Purchase #6 $178.96   13.290%   $202.7438   $202.74   $202.75   $202.70  
  Purchase #7 $78.69   5.436%   $82.9676   $82.97   $82.95   $83.00  
  7 purchase totals = $946.52       $1,043.5200   $1,043.52   $1,043.50   $1,043.60