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 $107.37   6.814%   $114.6862   $114.69   $114.70   $114.70  
  Purchase #2 $167.94   11.127%   $186.6267   $186.63   $186.65   $186.60  
  Purchase #3 $152.65   10.585%   $168.808   $168.81   $168.80   $168.80  
  Purchase #4 $45.78   10.493%   $50.5837   $50.58   $50.60   $50.60  
  Purchase #5 $216.75   6.736%   $231.3503   $231.35   $231.35   $231.40  
  Purchase #6 $107.48   8.452%   $116.5642   $116.56   $116.55   $116.60  
  Purchase #7 $163.52   6.374%   $173.9428   $173.94   $173.95   $173.90  
  7 purchase totals = $961.49       $1,042.5619   $1,042.56   $1,042.60   $1,042.60