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 $54.91   4.799%   $57.5451   $57.55   $57.55   $57.50  
  Purchase #2 $200.73   7.716%   $216.2183   $216.22   $216.20   $216.20  
  Purchase #3 $106.82   11.654%   $119.2688   $119.27   $119.25   $119.30  
  Purchase #4 $110.83   3.785%   $115.0249   $115.02   $115.00   $115.00  
  Purchase #5 $59.55   3.616%   $61.7033   $61.70   $61.70   $61.70  
  Purchase #6 $246.76   3.164%   $254.5675   $254.57   $254.55   $254.60  
  Purchase #7 $160.68   6.370%   $170.9153   $170.92   $170.90   $170.90  
  7 purchase totals = $940.28       $995.2432   $995.25   $995.15   $995.20