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 $124.52   3.404%   $128.7587   $128.76   $128.75   $128.80  
  Purchase #2 $26.56   4.168%   $27.667   $27.67   $27.65   $27.70  
  Purchase #3 $208.65   4.530%   $218.1018   $218.10   $218.10   $218.10  
  Purchase #4 $239.77   3.252%   $247.5673   $247.57   $247.55   $247.60  
  Purchase #5 $60.62   11.351%   $67.501   $67.50   $67.50   $67.50  
  Purchase #6 $236.84   3.543%   $245.2312   $245.23   $245.25   $245.20  
  Purchase #7 $104.48   13.735%   $118.8303   $118.83   $118.85   $118.80  
  7 purchase totals = $1,001.44       $1,053.6573   $1,053.66   $1,053.65   $1,053.70