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 $93.41   5.603%   $98.6438   $98.64   $98.65   $98.60  
  Purchase #2 $228.48   12.730%   $257.5655   $257.57   $257.55   $257.60  
  Purchase #3 $91.83   7.246%   $98.484   $98.48   $98.50   $98.50  
  Purchase #4 $236.72   7.173%   $253.6999   $253.70   $253.70   $253.70  
  Purchase #5 $22.55   11.235%   $25.0835   $25.08   $25.10   $25.10  
  Purchase #6 $48.48   13.137%   $54.8488   $54.85   $54.85   $54.80  
  Purchase #7 $216.75   12.142%   $243.0678   $243.07   $243.05   $243.10  
  7 purchase totals = $938.22       $1,031.3933   $1,031.39   $1,031.40   $1,031.40