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 $236.89   11.246%   $263.5306   $263.53   $263.55   $263.50  
  Purchase #2 $84.76   3.137%   $87.4189   $87.42   $87.40   $87.40  
  Purchase #3 $80.34   5.174%   $84.4968   $84.50   $84.50   $84.50  
  Purchase #4 $62.45   8.118%   $67.5197   $67.52   $67.50   $67.50  
  Purchase #5 $183.89   8.644%   $199.7855   $199.79   $199.80   $199.80  
  Purchase #6 $243.91   9.291%   $266.5717   $266.57   $266.55   $266.60  
  Purchase #7 $40.93   5.466%   $43.1672   $43.17   $43.15   $43.20  
  7 purchase totals = $933.17       $1,012.4904   $1,012.50   $1,012.45   $1,012.50