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 $60.67   5.839%   $64.2125   $64.21   $64.20   $64.20  
  Purchase #2 $102.52   5.317%   $107.971   $107.97   $107.95   $108.00  
  Purchase #3 $105.67   6.296%   $112.323   $112.32   $112.30   $112.30  
  Purchase #4 $155.92   11.557%   $173.9397   $173.94   $173.95   $173.90  
  Purchase #5 $232.53   6.670%   $248.0398   $248.04   $248.05   $248.00  
  Purchase #6 $222.25   6.813%   $237.3919   $237.39   $237.40   $237.40  
  Purchase #7 $232.71   5.768%   $246.1327   $246.13   $246.15   $246.10  
  7 purchase totals = $1,112.27       $1,190.0106   $1,190.00   $1,190.00   $1,189.90