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 $241.91   8.426%   $262.2933   $262.29   $262.30   $262.30  
  Purchase #2 $77.99   12.353%   $87.6241   $87.62   $87.60   $87.60  
  Purchase #3 $25.76   6.702%   $27.4864   $27.49   $27.50   $27.50  
  Purchase #4 $182.42   13.547%   $207.1324   $207.13   $207.15   $207.10  
  Purchase #5 $71.59   8.666%   $77.794   $77.79   $77.80   $77.80  
  Purchase #6 $142.60   5.326%   $150.1949   $150.19   $150.20   $150.20  
  Purchase #7 $208.60   13.775%   $237.3347   $237.33   $237.35   $237.30  
  7 purchase totals = $950.87       $1,049.8598   $1,049.84   $1,049.90   $1,049.80