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 $68.74   11.258%   $76.4787   $76.48   $76.50   $76.50  
  Purchase #2 $218.79   7.441%   $235.0702   $235.07   $235.05   $235.10  
  Purchase #3 $189.56   10.452%   $209.3728   $209.37   $209.35   $209.40  
  Purchase #4 $34.69   13.582%   $39.4016   $39.40   $39.40   $39.40  
  Purchase #5 $150.49   4.801%   $157.715   $157.72   $157.70   $157.70  
  Purchase #6 $113.72   6.123%   $120.6831   $120.68   $120.70   $120.70  
  Purchase #7 $236.99   9.413%   $259.2979   $259.30   $259.30   $259.30  
  7 purchase totals = $1,012.98       $1,098.0193   $1,098.02   $1,098.00   $1,098.10