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 $58.33   5.413%   $61.4874   $61.49   $61.50   $61.50  
  Purchase #2 $117.74   11.822%   $131.6592   $131.66   $131.65   $131.70  
  Purchase #3 $232.37   10.370%   $256.4668   $256.47   $256.45   $256.50  
  Purchase #4 $176.85   3.338%   $182.7533   $182.75   $182.75   $182.80  
  Purchase #5 $218.98   4.378%   $228.5669   $228.57   $228.55   $228.60  
  Purchase #6 $105.93   7.311%   $113.6745   $113.67   $113.65   $113.70  
  Purchase #7 $45.53   7.771%   $49.0681   $49.07   $49.05   $49.10  
  7 purchase totals = $955.73       $1,023.6762   $1,023.68   $1,023.60   $1,023.90