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 $117.62   4.624%   $123.0587   $123.06   $123.05   $123.10  
  Purchase #2 $217.67   13.404%   $246.8465   $246.85   $246.85   $246.80  
  Purchase #3 $218.97   7.619%   $235.6533   $235.65   $235.65   $235.70  
  Purchase #4 $211.71   6.649%   $225.7866   $225.79   $225.80   $225.80  
  Purchase #5 $109.41   7.834%   $117.9812   $117.98   $118.00   $118.00  
  Purchase #6 $93.94   3.315%   $97.0541   $97.05   $97.05   $97.10  
  Purchase #7 $27.87   5.482%   $29.3978   $29.40   $29.40   $29.40  
  7 purchase totals = $997.19       $1,075.7782   $1,075.78   $1,075.80   $1,075.90