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 $225.55   4.840%   $236.4666   $236.47   $236.45   $236.50  
  Purchase #2 $146.84   13.286%   $166.3492   $166.35   $166.35   $166.30  
  Purchase #3 $213.84   11.119%   $237.6169   $237.62   $237.60   $237.60  
  Purchase #4 $168.72   5.323%   $177.701   $177.70   $177.70   $177.70  
  Purchase #5 $145.28   4.569%   $151.9178   $151.92   $151.90   $151.90  
  Purchase #6 $11.84   4.783%   $12.4063   $12.41   $12.40   $12.40  
  Purchase #7 $45.99   13.151%   $52.0381   $52.04   $52.05   $52.00  
  7 purchase totals = $958.06       $1,034.4959   $1,034.51   $1,034.45   $1,034.40